Let's say my opponent (who is active player) summons a creature. I have an instant spell (unsummon) that can unsummon his creature.....but I can't target the creature when it is still a spell. I have to wait for the spell to resolve (and becomes a creature) before I can target it.
I wait till his spell resolves....but since he was the last player to cast a spell = he gets priority.
So I can't do anything until he either passes or casts another spell.....even though I have instants, and he only has sorceries.
Now my opponent casts a 'sacrifice creature to damage opponent' type sorcery...and I still can't use my Unsummon because sacrifice doesn't go on the stack.
SO, According to how Priority works....my opponent is able to cast 2 Sorceries faster that I can cast an instant......doesn't this seem idiotic? Or am I missing something here?
You got the gist of it right. But you are also somewhat wrong on the details. Your opponent gets priority after his creature spell resolved, because he is the active player, not because he was the last player to cast a spell. That particular condition to get priority is for responding, which ensures, that the player who casts a spell is always the first player allowed to respond to it. So that you can, for example, cast a copy spell on your own instant/sorcery.
As for the sacrifice, that largely depends on wether the sacrifice is part of the costs or part of the effects of the spell. Since costs are paid when the spell is being cast, the creature is gone before anyone can respond. If it is instead an effect, you could unsummon the creature in response, because the spell's effects happen on resolution.
It is also possible for a trigger to go off during the resolution or even afterwards but before anyone gets priority (state based actions), and that trigger would keep him from casting a sorcery. That opens a window for you to unsummon.
Remember, instant doesn't mean you get to cast your spell whenever, the conditions are just much loser than for the other card types: you only have to have priority.
In general, after a creature spell resolves, it enters the battlefield and the active player gets priority (C.R. 608.3, 117.3b) and can immediately use it to cast sorcery spells (assuming it's the player's main phase and the stack isn't empty [C.R. 117.1a]) — unless triggered abilities have triggered, in which case any abilities that have just triggered will go on the stack and your opponent won't be able to cast any noninstant spells at the moment since the stack isn't empty (C.R. 117.3b, 117.5, 606.3). If that happens, you will eventually get priority to cast instant spells such as Unsummon before the stack becomes empty again (C.R. 117.3d, 117.1b). See also this submission on Reddit.
Active Player summons a creature (that has a 'non-tap' ability)....if you can't counter it, you have to let it resolve*.
Since the Active Player is the one who gets priority (except end step, I think) = they can then use the ability of the creature they just summoned.
ONLY THEN can you use your unsummon....which can't prevent the 'activate ability', but can mess with the target of said ability.
I think I got it. Thanks everyone!
*If the active player is casting a summon creature, you could put your 'unsummon' on the stack targeting a creature that's already on the board = nothing to really do with the creature being summoned, but it would allow you to use your unsummon against a target already on the board.
Players get priority during all steps and phases of the turn with the exceptions of the untap step of the beginning phase, and the cleanup step of the end phase. The end step is the first step of the end phase, and is usually the last time players get to act during a turn.
I wait till his spell resolves....but since he was the last player to cast a spell = he gets priority.
So I can't do anything until he either passes or casts another spell.....even though I have instants, and he only has sorceries.
Now my opponent casts a 'sacrifice creature to damage opponent' type sorcery...and I still can't use my Unsummon because sacrifice doesn't go on the stack.
SO, According to how Priority works....my opponent is able to cast 2 Sorceries faster that I can cast an instant......doesn't this seem idiotic? Or am I missing something here?
As for the sacrifice, that largely depends on wether the sacrifice is part of the costs or part of the effects of the spell. Since costs are paid when the spell is being cast, the creature is gone before anyone can respond. If it is instead an effect, you could unsummon the creature in response, because the spell's effects happen on resolution.
It is also possible for a trigger to go off during the resolution or even afterwards but before anyone gets priority (state based actions), and that trigger would keep him from casting a sorcery. That opens a window for you to unsummon.
Remember, instant doesn't mean you get to cast your spell whenever, the conditions are just much loser than for the other card types: you only have to have priority.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
EDIT: Clarification after comment 5 was posted.
Active Player summons a creature (that has a 'non-tap' ability)....if you can't counter it, you have to let it resolve*.
Since the Active Player is the one who gets priority (except end step, I think) = they can then use the ability of the creature they just summoned.
ONLY THEN can you use your unsummon....which can't prevent the 'activate ability', but can mess with the target of said ability.
I think I got it. Thanks everyone!
*If the active player is casting a summon creature, you could put your 'unsummon' on the stack targeting a creature that's already on the board = nothing to really do with the creature being summoned, but it would allow you to use your unsummon against a target already on the board.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)