Priority and the Stack
Priority and the stack are two of the most important aspects of the rules of Magic. Practically every action in the game involves them, either directly or indirectly. However, there are a number of players, both new and old, that do not understand the subtleties of these two things. In this article, I will try to explain the stack and the priority system, starting with very simple rules and then moving on to more complex rules. I think the problem is that there are so many rules that it can sometimes be overwhelming. If players can understand the basics, the exceptions and peculiarities become much easier to pick up.
What is the stack?
The stack is how the game of Magic decides and regulates when spells and abilities resolve (meaning, do their effect, such as a Lightning Bolt dealing its 3 damage). The name comes from the actual stacking of the cards on the table. In fact, this is a good way to keep track of what order things are happening and I encourage you to do it whenever things start getting complicated. Let’s go through some examples and see how this thing works.
Example #1: Player A has Flying Men and a Forest in play and a Giant Growth in his hand. Player B has a Mountain in play and a Lightning Bolt in his hand. Player B would very much like to kill Flying Men. So, Player B plays his Lightning Bolt, targeting Flying Men. Player A doesn’t like this very much, so he plays Giant Growth “in response”, targeting Flying Men, hoping that he will save them. What happens?
Ok, let’s take this one step at a time. Whenever a player plays a spell, that card goes on top of the stack. So, when Player B plays his Lightning Bolt, it goes on top of the stack (which was empty). The stack therefore looks like this:
Top of stack
Lightning Bolt
Bottom of stack
Lightning Bolt has to sit there for a moment because a player still wants to do something. A spell does not resolve immediately. Instead, both players have to say “I won’t want to do anything right now” before a spell resolves (I’ll address the technical points of this in a moment). So, Lightning Bolt stays on the stack for now. After Player B played his Lightning Bolt, Player A played his Giant Growth. The expression for this would be “Player A is playing Giant Growth in response to Lightning Bolt. So, Giant Growth goes on top of Lightning Bolt on the stack. The stack now looks like this:
Top of stack
Giant Growth
Lightning Bolt
Bottom of stack
Again, Giant Growth, like Lightning Bolt earlier, does not resolve immediately; both players have to have the opportunity to play a spell if they want to before a spell can resolve. Both players decide that they don’t want to do anything else right now. So, the rule is: when both players decide that they don’t want to do anything, the spell on top of the stack resolves and only the spell on top of the stack resolves. In this case, it is Giant Growth. So, Giant Growth resolves and Flying Men become a staggering 4/4.
Magic is less like this than you thought.
We’re not done yet though because Lightning Bolt is still on the stack, waiting to resolve. Both players again say they don’t want to do anything, so Lightning Bolt resolves and deals 3 damage to Flying Men. Unfortunately for Player B, Flying Men are bigger now with their toughness of 4, so Flying Men will remain in play. Tough break for Player B.
Example #2:
This time, Player A still has Flying Men in play and let’s just assume each player has enough mana to do whatever he wants to do. Player B, determined to get Flying Men, again plays Lightning Bolt targeting Flying Men. This time, Player A doesn’t have Giant Growth, although he does have Brainstorm, a much beloved staple of the Vintage format. Player A plays Brainstorm. The stack looks like this:
Top of stack
Brainstorm
Lightning Bolt
Bottom of stack
Both players decide they don’t want to do anything, so Brainstorm resolves. Player A draws 3 cards and then puts 2 back on top of his library. Fortunately for Player A, he drew Counterspell. But, can Player A use his Counterspell to counter Lightning Bolt?
Yes, he can. From the rule I gave in example #1, the top spell of the stack resolves when neither player wants to do anything and only the top spell of the stack resolves. But Player A wants to do something (in this case, play Counterspell), so he gets the opportunity to do that. Player A plays Counterspell, targeting Lightning Bolt.
Top of stack
Counterspell
Lightning Bolt
Bottom of stack
Both players again decide that they don’t want to do anything else. Therefore, the spell on top of the stack resolves, which is Counterspell. Yes, that’s right, Player A managed to get two spells played and resolved before Player B got a chance for his Lightning Bolt resolve. Unfortunately for Player B, Counterspell is going to counter Lightning Bolt, so Flying Men will again avoid certain doom.
Are you with me so far? I hope so. As you may have noticed, I’ve been using this vague language of “nobody wants to do anything else, so the spell on top of the stack resolves.” I did this for simplification to avoid adding too many steps along the way. The way you figure out who gets to play what and when they get to play it is under a “system of priority.”
What is priority?
”It’s my turn to play a spell!”
“No, it’s my turn!”
When a player has priority, the player has two choices:
1) play a spell, or
2) pass priority to the other player
That’s it, nothing else (well, that’s not really it, but that’s it for right now). To go back to example #1, Player A had Flying Men in play and Player B wanted to kill them with Lightning Bolt. Let’s say Player A started with priority. Player A decided he didn’t want to do anything, so he passed priority. Player B, having priority, chooses to play Lightning Bolt. Simple enough, but who has priority now? Well, did Player B pass priority? No, he chose to play a spell. Therefore, Player B still has priority, even though he just played a spell.
The rule is: whenever a player plays a spell, that player gets priority again until he passes it. So, in theory, a player could play four Lightning Bolts in a row, with a kickered Urza’s Rage on top of that if he wanted to. As unfair as this might seem, it does not generally give the player any special advantage. Each spell still resolves one at a time; the fact that the player played the spells one after the other does not give the spells any special status. So, regardless of how many spells a player plays in a row, the other player will always get a chance to respond.
Going back to the example, Player B kept priority after playing Lightning Bolt. But, Player B didn’t want to do anything else, so he passed priority to Player A. Player A again faces the choice: play a spell or pass priority. The situation is different now, however. Remember earlier how I mentioned that “if neither player wants to do anything, the top spell on the stack resolves”? Well, when both players pass priority in a row, that’s how the game knows that nobody wants to do anything. If Player A had chosen to pass rather than play his Giant Growth, his Flying Men would have died because the Lightning Bolt would have resolved.
But, that’s not how it happened, so Player A played Giant Growth and then Giant Growth resolved after both players passed priority in a row. So who has priority now? Alas, things have to get more complicated still. When a spell resolves, the active player (the player whose turn it is) gets priority, regardless of whose spell just resolved. Note a very important distinction here:
Whenever a player plays a spell, that player keeps priority.
Whenever a spell resolves, the active player gets priority.
If you can get these two rules down, you will be well on your way to getting all this stack and priority stuff figured out. To answer the question posed above, it depends on whose turn it is. One thing that is important to note about keeping priority after playing a spell is that players often assume that a player is passing priority after playing a spell. As a practical matter, if you intend to play one spell right after the other without passing priority, you probably need to say something like “I’ll Lightning Bolt Flying Men and in response to that I’ll Shock you.” Otherwise, the game may skip ahead when you don’t want it to.
Don’t let the silence throw you from
what’s really going on.
Let’s see if we can put it all together now.
Example #3:
Player A has Flying Men in play, has priority, and it is his first main phase. Again, each player has enough mana to play whatever he wants to play. After all these attempts by Player B to kill Flying Men, Player A is concerned, so he hopes to dig up an answer by playing Ancestral Recall, targeting himself.
Top of stack
Ancestral Recall (targeting Player A)
Bottom of stack
Player A passes priority. Player B does not like Player A’s attempt to abuse Vintage brokenness, so he plays Counterspell, targeting Ancestral Recall, and he passes priority.
Top of stack
Counterspell (targeting Ancestral Recall)
Ancestral Recall (targeting Player A)
Bottom of stack
Because Ancestral Recall is so important to resolve, Player A plays Mystical Tutor and passes priority.
Top of stack
Mystical Tutor
Counterspell (targeting Ancestral Recall)
Ancestral Recall (targeting Player A)
Bottom of stack
Player B passes priority back and Mystical Tutor resolves. Player B tutors up Cancel and puts it on top of his library. The stack looks like this:
Top of stack
Counterspell (targeting Ancestral Recall)
Ancestral Recall (targeting Player A)
Bottom of stack
Player A has priority now (because it is his turn). Player A plays the last card in his hand, Brainstorm, to try get Cancel off the top of his deck. Player A passes priority. However, Player B’s plan has finally come together. Player B plays Lightning Bolt, targeting Flying Men, and passes priority.
Top of stack
Lightning Bolt (targeting Flying Men)
Brainstorm
Counterspell (targeting Ancestral Recall)
Ancestral Recall (targeting Player A)
Bottom of stack
The less popular Falling Men.
Top of stack
Brainstorm
Counterspell (targeting Ancestral Recall)
Ancestral Recall (targeting Player A)
Bottom of stack
Player A gets priority again after Lightning Bolt resolves, because it is his turn. It doesn’t matter whose spell just resolved. Player A passes priority and Player B passes priority. Brainstorm resolves. Player A draws Cancel, as expected, and puts the other two cards back on top of his library.
Top of stack
Counterspell (targeting Ancestral Recall)
Ancestral Recall (targeting Player A)
Bottom of stack
Player A gets priority because a spell resolved and it is his turn. He plays Cancel, targeting Counterspell.
Top of stack
Cancel (targeting Counterspell)
Counterspell (targeting Ancestral Recall)
Ancestral Recall (targeting Player A)
Bottom of stack
Player A passes and Player B passes. Cancel resolves, countering Counterspell.
Top of stack
Ancestral Recall (targeting Player A)
Bottom of stack
Ancestral Recall finally resolves and Player A draws his 3 cards. Unfortunately, it is already too late for Flying Men.
The stack is empty now and Player A has priority. He passes priority and Player B passes priority back. There isn’t a spell on the stack to resolve, so what happens? Whenever both players pass in a row with an empty stack, the game moves on to the next step, which in this case would be the “beginning of combat step” since we were previously in the first main phase. This tends to be important during the combat phase, although it can be important at other times.
As I mentioned at the beginning of the article, I took some liberties with the rules to explain some things in a simpler way. There are a few things that, while complicating, are important enough that you should know. First, there are things other than spells that use the stack. Activated abilities (like Prodigal Sorceror’s deal one damage ability) use the stack just like spells. Don’t let the fact that there is not a physical card on the stack confuse you; it works in exactly the same way as a physical spell card. Triggered abilities (like Primordial Sage’s card draw ability) also use the stack (precisely how triggered abilities work is beyond the scope of this article). Just know that whenever a trigger event occurs, that ability goes on the stack and then the player that has priority gets a chance to do whatever he is going to do. As a short example, if Player A plays Flying Men and has Primordial Sage in play, the card drawing ability will go on the stack before Player A would get a chance to respond to his own Flying Men. If Player A then responded to his own Flying Men with Brainstorm, the stack would look like this:
Top of stack
Brainstorm
Primordial Sage triggered ability
Flying Men
Bottom of stack
The rules of when a player can play spells still apply. A player can only play sorcery and creature spells during his main phase and only if the stack is empty.
While this stack stuff is pretty exciting, there are some things in Magic that don’t use the stack. While there are number of things that don’t use the stack, the two most important ones that you should be concerned with right now are mana abilities and playing a land. A mana ability is any activated ability that puts mana into your mana pool (tapping a Forest for mana being a very simple example). Rather than having to wait for your mana, you get it immediately after using the ability and without passing priority. When a player plays a land, that action does not use the stack. Instead, the land just comes into play and the player keeps priority. Note the distinction, however, between playing a land and things that put a land into play. If a player plays Untamed Wilds, that spell will use the stack just like any other, as will the ability from fetching an Island with Polluted Delta. Also, lands can only be played when the stack is empty.
That about wraps up the basics, so let’s try some problems.
Problem #1: Player A controls Squire. During Player A’s turn, Player A plays Giant Growth targeting the Squire. In response, Player B plays Shock. What happens to Squire?
Squire will be destroyed. Giant growth goes on the stack first. Before Giant Growth resolves, Player B plays Shock in response, so the stack looks like this:
Top of stack
Shock
Giant Growth
Bottom of stack
Since Shock is on top of the stack, it resolves first. Shock deals 2 damage to Squire, killing it. Giant Growth then fizzles (meaning, it is countered on resolution because all of its targets are illegal), and does nothing.
Top of stack
Shock
Giant Growth
Bottom of stack
Since Shock is on top of the stack, it resolves first. Shock deals 2 damage to Squire, killing it. Giant Growth then fizzles (meaning, it is countered on resolution because all of its targets are illegal), and does nothing.
Problem #2: Player A controls Goblin Hero. During Player A’s turn, Player A passes priority to Player B. Player B plays Brainstorm and Brainstorm resolves. Player B then plays Sudden Shock, targeting Goblin Hero. Player A says he wanted to play Extirpate, targeting the Sudden Shock in Player B’s graveyard. Who is right?
Player A is right. After a spell resolves, the active player (the player whose turn it is) gets priority, regardless of who controlled the spell that resolved. Therefore, Player A always had priority after Brainstorm resolved and Player B never had it. Player B therefore could not play Sudden Shock yet. Player A will get to play Extirpate (which will resolve first due to split second), and will remove the Sudden Shocks from Player B’s graveyard and Player B’s hand. Too bad for Player B.
Problem #3: Both players are at 1 life. Player A controls Prodigal Sorcerer. Player A taps his Prodigal Sorcerer to deal one damage to Player B. Player A says he wins because he dealt one damage to Player B. Player B says that the damage hasn’t been dealt yet. He tries to play Brainstorm in response. Over Player A’s protests that the game is over, Player B draws 3 cards and puts 2 back. Player B then plays Lava Dart, targeting Player A. Who wins?
Player B wins. Prodigal Sorcerer’s ability, just like most anything else, uses the stack and does not resolve immediately. So, Player B’s plays were legal.
Problem #4: Player A has floating in his mana pool (it was left over from a Dark Ritual he played earlier). Player A forgets that the has in his mana pool and passes priority. Player B taps a Mountain and then plays Shock, targeting Player A. Player A remembers that he has floating in his mana pool and says that he is playing Extirpate, targeting the Shock in Player B’s graveyard, in response to Player B tapping his Mountain for mana. What happens?
Shock will go on the stack before Player A gets to play Extirpate. This is because mana abilities don’t use the stack and resolve immediately. Player A will still get the chance to play Extirpate, it just won’t affect the Shock that is already on the stack.
In summary, there are basically three things to keep in mind:
1) When a player plays a spell or ability, that player keeps priority.
2) When a spell resolves, the active player (the player whose turn it is), gets priority.
3) The thing on top of the stack resolves when both players pass in a row.
I am curious as to how helpful this article was. If you found it useful (or if you found it useless), please let me know in the forums, as I am considering writing more articles like this one. Have an idea for a tutorial? Let me know. Thanks for reading.
Top of Stack
Doom Blade (targeting Kor Spiritdancer)
Kor Spiritdancer's triggered ability (draw a card)
Canopy Cover (targeting Kor Spiritdancer)
Bottom of Stack
Assuming nobody does anything else and passes over and over, Doom Blade resolves and destroys Kor Spiritdancer. Kor Spiritdancer's triggered ability resolves and Player 1 draws a card. Finally, Canopy Cover tries to resolve, sees that its target is no longer there, and is countered on resolution due to all of its targets being illegal ("fizzles").
Note that Canopy Cover technically only gets countered and goes to the graveyard when it tries to resolve, not immediately upon Kor Spiritdancer going to the graveyard. I have a hard time conceiving of a situation where this would matter, though (I suppose there could be a situation where the number of cards in a graveyard was important for threshold being active).
I registered specifically for this article.
Just so you know, I am impressed. You are articulate, informative, and I can tell you really enjoy this game. So, Thank you.
Anyway, back to my question...
Admittedly, after an hour of reading, my head started spinning a little.
Example # 2
So Player A gets to keep Priority after Brainstorm resolves and is able to cast the Counterspell he obtained, Why?
Because it is his turn?
Player 2 Counters with Lightning Bolt
Player 1 Pays 3 mana (1colorless, 1green, 1black) to activate his ability to sacrifice itself to damage both players '3'
Player 2 argues that Lightning bolt stops Jarad's summon from resolving
Player 1 argues that it is not a counter spell it is a damage spell so it does resolve and therefore has a +1/+1 and is able to put its ability on the stack especially because it doesn't have to tap for it meaning summoning sickness is not a factor neither.
Who is right and who is wrong?
Looking forward to your response!!
Player A will have the chance to play his Counterspell before Lightning Bolt resolves, regardless of whose turn it is. The only difference would be that if it's Player A's turn, then he would get priority first after Brainstorm resolved as opposed to second if it were Player B's turn. In that example, Player B would pass then Player A could go "oh, I want to play Counterspell before Lightning Bolt resolves," and he'll simply respond by playing Counterspell (targeting Lightning Bolt). Both players then pass and Counterspell resolves, countering Lightning Bolt.
As a practical matter, it very rarely matters whose turn it is and therefore who gets priority first after a spell resolves. In most cases, it's a question of "when did both players pass priority so we can resolve the top thing on the stack?"
Question 2:
The 1/1 creature will die will die. In this example, Giant Growth is on top of Lightning Bolt on the stack, so Giant Growth will resolve first. Ok, so the 1/1 (let's say it's Merfolk of the Pearl Trident becomes 4/4. Next, Lightning Bolt resolves and the Merfolk have 3 damage on him. They've only been dealt 3 damage this turn but have 4 toughness, so they'll stick around for a bit longer. That damage stays with the Merfolk until the very end of the turn. But, you ping the Merfolk for one more damage with Prodigal Sorcerer later in the same turn. The game sees that the Merfolk have been dealt damage equal to or greater than their toughness (in this case, 4 damage), and are destroyed.
For more info on how creatures die, see my other article:
Magic 101: How Creatures Die (June 25, 2010)
http://www.mtgsalvation.com/articles/15275-magic-101-how-creatures-die
NOTE: The Legend Rule has changed since that article was published. Each player can have one copy of the same legend on his or her own side now without either legend dying. Everything else should still be correct, though.
Question 3:
I'm a little confused on precisely what you're asking. Could you please clarify your question? Is the Lightning Bolt targeting Jarad or another creature you control? If it's attempting to target Jarad while he is still a spell on the stack, that won't work and is illegal -- Lightning Bolt can only target creatures that are already on the battlefield, not while they're still spells on the stack.
Yes, thunderbolt targets Jarad.
So after Jarad's summon resolves Player 1 pays his ability cost and then player 2 Lightningbolts, that means Lightning Bolt resolves first before he can sacrifice himself, successfully preventing his ability from resolving, right?
What if Lightning bolt was cast first and then player 1 pays his ability cost? Does that mean his ability to target sacrificing himself resolves first?
Because I'm also wondering if a creature can be sacrificed for its effects as soon as its summon resolves even with summoning sickness.
BTW, you are awesome.
Ok, so Player 1 has just played Jarad, Golgari Lich Lord and it resolved. It must be Player 1's turn since he just played Jarad (barring something crazy), so he'll have priority. At this point, Player 1 could activate activate Jarad's ability to sacrifice a creature and put that ability on the stack. But, note that Jarad's ability says you have to sacrifice another creature to use it, so you can't sacrifice Jarad to himself (which seems to be what you want to do).
So, let's change the example a little and assume Player 1 also has Merfolk of the Pearl Trident on the battlefield. Once Jarad comes into play, Player 1 will have priority (it's his turn and a spell resolved) and can immediately activate Jarad's ability. When he does this, the Merfolk are immediately sacrificed and placed in the graveyard as part of the cost of activating Jarad's ability. The Jarad ability goes on the stack, so the stack looks like this:
Top of Stack
Jarad's activated ability
Bottom of Stack
Player 1 passes priority. At this point, Player 2 cannot target the Merfolk with Lightning Bolt because it's already in the graveyard. Let's assume Player 2 has Terminate and he plays it targeting Jarad (who is now 5/5, by the way, since Player 1 has two creatures in the graveyard instead of one). Jarad's ability doesn't resolve yet because both players haven't passed in a row, so Terminate is now placed on the stack above the activated ability:
Top of Stack
Terminate (targeting Jarad)
Jarad's activated ability
Bottom of Stack
Player 2 passes, Player 1 passes, and Terminate resolves, destroying Jarad. The stack now looks like this:
Top of Stack
Jarad's activated ability
Bottom of Stack
Destroying Jarad won't stop Jarad's ability from resolving and causing both players to lose 1 life. Abilities generally exist independently of their sources so destroying their sources won't stop them from resolving. Think of it as the same thing as shooting a guy who's already thrown a hand grenade. Yeah, the thrower is dead, but the grenade will still explode. To stop the activated ability, you'll need something like Stifle that counters abilities.
So let's consider another example. Same set up with Jarad having just come onto the battlefield and Player 1 also controlling Merfolk of the Pearl Trident. This time Player 1 just passes priority instead of activating Jarad's ability. Player 2 plays Lightning Bolt, targeting Merfolk of the Pearl Trident. The stack looks like this:
Top of Stack
Lightning Bolt (targeting Merfolk of the Pearl Trident)
Bottom of Stack
Player 2 passes. Player 1 sees that his Merfolk are doomed, so in response he sacrifices his Merfolk to Jarad. The Merfolk are immediately placed in the graveyard. The stack now looks like this:
Top of Stack
Jarad's activated ability
Lightning Bolt (targeting Merfolk of the Pearl Trident)
Bottom of Stack
Player 1 passes and Player 2 passes. Jarad's ability resolves and both players lose 1 life. The stack now looks like this:
Top of Stack
Lightning Bolt (targeting Merfolk of the Pearl Trident)
Bottom of Stack
Player 1 passes, Player 2 passes. Lightning Bolt tries to resolve, but the game sees that its target is now illegal because the Merfolk are already in the graveyard. Lightning Bolt is countered on resolution because all of its targets are illegal and does nothing (in the old days we used to call this "fizzling"--I'm not sure if they still use this term). Player 2 doesn't get a chance to change the target or anything at this time--Lightning Bolt just goes to the graveyard and does nothing.
Finally, regarding summoning sickness. Summoning sickness means a player can't attack with a creature or activate any of its abilities with the tap symbol (or the untap symbol) as part of the cost unless that player has continuously controlled that creature since the beginning of his most recent turn. In the normal case, this just means you can't attack or activate a tap symbol ability of a creature the same turn you played the creature.
So, let's look at Jarad. He has an activated ability, but it doesn't have a tap symbol in the cost. For this reason, you can use Jarad's activated ability the moment he comes into play -- you don't have to wait until the next turn. However, with a card like Scourge of Skola Vale, you could not activate that ability the turn the Scourge comes into play because it has the tap symbol in its cost. Both involve sacrificing another creature you control, but since the Scourge has the tap symbol, he has to wait around until your next turn before he gets to start devouring other creatures.
I hope this is helpful. Like I said above, if I was confusing or was unclear about something, feel free to ask me to clarify.
;D
It's always great reading from you.
So just to confirm, with the jarad-lightningbolt example we've been using, there is no way I can stop Jarad from using that ability unless I have stifle?
I think the answer is "Yes, there is no way."
I am messing with this cool-clunky style program called LackeyCCG. We should play sometime soon.
Regarding your question, fortunately, I happened to write an article on triggered abilities as well:
Magic 101: Triggered Abilities (April 1, 2008)
http://www.mtgsalvation.com/articles/15667-magic-101-triggered-abilities
Check out the article and see if you can explain how you think it will work out. I promise that I'll give the answer once you've given it a shot, though.
The situation does work out in your favor, but not for the reasons you say.
So, Kor Skyfisher comes into play. The game sees this and both Kor Skyfisher and Prison Term trigger at the same time. A couple of things need to be decided at this point: 1) Which trigger goes on the stack first? and 2) What are the targets for those triggers going to be? Note: the triggers will both go on the stack before either player gets priority or a chance to play anything new. By "Triggered abilities go on the stack when a player would gain priority", I meant that "Instead of a player gaining priority, all triggered abilities go on the stack and then a player gains priority." So, we have to deal with both triggers right now before anybody gets a chance to play anything.
How do we decide which trigger goes on the stack first? Quoting from the article:
The game has a rule for handling this too, called the “APNAP rule”. APNAP stands for “active player, nonactive player," meaning that the active player puts all of his triggers on the stack first, and then the nonactive player puts all of his triggers on the stack second. . . . the controller of a triggered ability is the controller of the thing that created the triggered ability.
So, the active player (the player whose turn it is) puts names his target and puts his triggered ability on the stack first. In this case, assuming your brother doesn't have Crucible of Worlds in play or anything fancy like that, it will be his turn so he is the active player and has to pick a target for his triggered ability first. Let's assume your brother's other creature enchanted with Prison Term is Squire and he targets that and puts the triggered ability on the stack. At this point, you put your triggered ability on the stack for Prison Term. You see that your brother targeted Squire, so you smartly choose to target Kor Skyfisher with Prison Term's triggered ability. So, the stack looks like this:
Top of Stack
Prison Term's triggered ability (targeting Kor Skyfisher)
Kor Skyfisher's triggered ability (targeting Squire)
Bottom of Stack
Now your brother gets priority (since it's his turn). You both pass and Prison Term's triggered ability resolves and moves to Kor Skyfisher. Kor Skyfisher's triggered ability resolves and returns Squire to your brother hand.
So, you get the better of this one.
Edit: see further clarification two comments down...
I made some mistakes; this is wrong. Please see below comments.
You're almost right, but let me clarify--I was a little imprecise in my language above.
Both players can still respond to the triggers (like any other spell or ability) and they still resolve one at a time after both players pass (like any other spell or ability).
So, with this stack:
Top of Stack
Prison Term's triggered ability (targeting Kor Skyfisher)
Kor Skyfisher's triggered ability (targeting Squire)
Bottom of Stack
At this point, your brother will get priority again because he was the last person to play a spell (the Kor Skyfisher). He could cast Stifle to counter your Prison Term's triggered ability or he could cast Mage's Guile on his Skyfisher to give it shroud and to prevent Prison Term's triggered ability from moving the Prison Term to Kor Skyfisher. But, assuming neither of you have any response and pass, only Prison Term's triggered ability will resolve and then you'll have a stack that looks like this:
Top of Stack
Kor Skyfisher's triggered ability (targeting Squire)
Bottom of Stack
Once again, at this point, you'll both get the chance to play spells and abilities, though your brother will get priority first since it is his turn. After he passes, you could cast Voidslime on the triggered ability or you could cast Veil of Secrecy on your Squire (you could also have done this earlier before Prison Term's triggered ability resolved as well).
The long and the short of it is that the triggered abilities use the stack like other spells and abilities and can be responded to like other spells and abilities.
Also, apologies for not responding sooner--I was away from home for a couple of days.
I made some mistakes; this is wrong. Please see below comments.
If you look at the rulings of Kor Skyfisher, you’ll see that it’s ability doesn’t target a permanent, but rather gives you a choice when it resolves.
It means that according to the triggered abilities’ priority Prison Term's triggered ability resolves first and you may target Kor Skyfisher, but when Kor Skyfisher’s triggered ability resolves second your brother choses the permanent which he bounces, meaning he can (and probably will) choose the permanent w/ Prison Term, sending your enchantment to the graveyard unless you’ve used something that cancels abilities.
I mean, no disrespect, I think that everything is in order regarding the stack, but the thing is that Kor Skyfisher’s ability functions differently.
So, here's the setup once again. Chris's brother has Squire in play enchanted with Chris's Prison Term. Chris's brother plays Kor Skyfisher. Assuming both players try to play optimally, who gets the better of this situation?
If you've read the above incorrect answers I gave, let me first point out that neither Prison Term nor Kor Skyfisher targets. This means that decisions for their abilities will all be made on resolution; you don't have to decide anything when they trigger.
So, Kor Skyfisher comes into play and both Prison Term and Kor Skyfisher trigger. How do we decide which trigger goes on the stack first? Quoting from my article, Triggered Abilities (http://www.mtgsalvation.com/articles/15667-magic-101-triggered-abilities):
The game has a rule for handling this called the “APNAP rule”. APNAP stands for “active player, nonactive player," meaning that the active player puts all of his triggers on the stack first, and then the nonactive player puts all of his triggers on the stack second. . . . the controller of a triggered ability is the controller of the thing that created the triggered ability.
So, the active player (the player whose turn it is) puts his triggered ability on the stack first. In this case, since Chris's brother played Kor Skyfisher it probably is his turn (assuming no funny business like Teferi, Mage of Zhalfir) so he is the active player and puts his triggered ability on the stack first. Next, Chris puts his triggered ability on the stack for Prison Term. So, the stack looks like this:
Top of Stack
Prison Term's triggered ability
Kor Skyfisher's triggered ability
Bottom of Stack
Assuming both players pass, Prison Term's triggered ability will resolve. Chris gets to decide at this point whether to move Prison Term to Kor Skyfisher because it says he may move it---he isn't required to. Let's assume he moves it to Kor Skyfisher.
Now the stack looks like this:
Top of Stack
Kor Skyfisher's triggered ability
Bottom of Stack
Assuming both players pass, Kor Skyfisher's triggered ability resolves. Chris's brother now gets to choose which permanent to return to his hand. Seeing that the Kor Skyfisher is enchanted with Prison Term, he chooses to return Kor Skyfisher and Prison Term goes to the graveyard since the thing it was enchanting, Kor Skyfisher, is now gone. Note that the outcome is basically the same here even if Chris chooses to leave Prison Term on Squire instead of moving it. When Kor Skyfisher's triggered ability resolves, Chris's brother can just choose to return Squire instead, again causing Prison Term to go to the graveyard. Finally, note that Chris's brother can't choose to return Prison Term to Chris's hand (if he wanted to for some reason)---Chris still controls Prison Term even though it is enchanting his opponent's creature.
So, to answer the question: Chris's brother will get the better of this situation. He'll be left with either Squire or Kor Skyfisher in play and Prison Term will be in the graveyard.
Thanks
The combat phase has the following steps:
Beginning of combat step
Declare attackers step
Declare blockers step
Combat damage step
End of combat step
So, your question is "Can I use Giant Growth or Royal Assassin's activated ability during the combat phase and have them still be effective?" The short answer is "Yes, but you'll want to use them before the combat damage step begins, meaning your last opportunity is during the declare blockers step." Let's look at an example.
Support Player A has Squire in play and Giant Growth in hand and Player B has Goblin Hero in play and we're in the first main phase of Player A. Both players pass and we move to the beginning of combat step. Both players pass again. We move to the declare attackers step. At this point, Player A declares Squire as an attacker. Both players pass and we move to the declare blockers step. Player B declares that Goblin Hero is blocking Squire. If both players pass priority after Goblin Hero is declared as a blocker, combat damage will be dealt immediately and it will be too late for Player A to save Squire. So, instead, during the declare blockers step, Player A plays Giant Growth, targeting Squire. Both players pass, Squire deals 4 damage to Goblin Hero, Goblin Hero deals 2 damage to Squire, and Goblin Hero dies while Squire lives.
Under the old rules (which are described above and are no longer the current rules), instead of the damage being dealt immediately, the damage would go on the stack like anything else at the beginning of the combat damage step and both players had the chance to respond to it with things like Shelter. As a practical matter this won't matter most of the time, as Player B could have played Shelter in response to Giant Growth during the declare blockers step. It's just that rules-lawyers will try to trick you and have combat damage be dealt when maybe you didn't intend for it to be dealt.
What about Royal Assassin? Suppose Player A has Squire in play and Player B has Royal Assassin in play. Again, Player A declares Squire as an attacker and taps Squire during the declare attackers step. After Player A passes, Player B can simply activate Royal Assassin targeting the now-tapped Squire and destroy him. Squire won't deal any damage because he'll be destroyed before the game reaches the combat damage step.
If you find this confusing, my advice is to just make clear to your opponent that you want to do these things before damage is dealt. Whenever blockers are declared, immediately after that is your last chance to do anything sneaky before damage is dealt. If both players pass, damage will be dealt and it will be too late.