Would it be possible to disrupt the Mikaeus, the Unhallowed + Triskelion combo by adding extra +1/+1 counters to the Triskelion as priority passes, so that it has a counter as it dies and does not trigger Mikaeus, the Unhallowed? I'm unclear on the trigger/priority/response interactions here. For purposes of this discussion, assume I can add counters indefinitely (such as with Ghave, Guru of Spores.
In general, no. If +1/+1 counters are put on a creature while a spell or ability resolves, the creature will generally remain on the battlefield after the spell or ability resolves and the active player will get priority to activate abilities, including Triskelion's ability (C.R. 116.3b, 116.5, 704.5f-h, 116.1b).
EDIT (Jan. 15): Clarification.
EDIT (Apr. 5): Added rule citation.
EDIT (May 16): Edited post to conform to "put" rather than "place" convention introduced in Amonkhet.
If my assertion vs. my opponent is correct (and that's, mind you, IF!) the sequence MIGHT go something like this:
0. Assume 3/3 Triskelion with 3 damage marked (1/1 naturally, +1 from Mikaeus, +1 counter.)
1. Opponent removes final counter to activate Triskelion, passes priority.
2. I activate ability to add 1 counter to Triskelion, pass priority. Opponent cannot yet remove this counter, because it hasn't resolved.
3. Both players have passed, first ability on stack resolves: Triskelion gets a +1/+1 counter and is again a 3/3 with 3 damage marked.
4. Opponent would receive priority, (116.3b) but first state-based actions are checked (704.3) and Triskelion dies (704.5g) and goes to the Graveyard before
opponent receives priority.
5. Undying tries to trigger (603.4) and fails because Triskelion had a +1/+1 counter when it last existed (either during Step 3 or all the way back in Step 0). Combo is disrupted.
BUT I could be misinterpreting the rules. Can somebody check my math?
0. Assume 3/3 Triskelion with 3 damage marked (1/1 naturally, +1 from Mikaeus, +1 counter.)
This is already wrong. A 3/3 with 3 damage marked will be desroyed by state based actions before any player can do anything. So if this occurs, the Triskelion will not come back.
The combo works by making Triskelion shoot itself twice with its last two counters. This way, there is a 2/2 Triskelion with no counters on the field and it eventually will have two damage marked, destroying it, and triggering undying. If you somehow place another counter before Triskelion dies, your opponent can simply remove it to deal damage to something, or target Triskelion itself. More +1/+1 counters are just more fuel for the fire.
Your scenario is faulty because the damage marked on Triskelion (3 damage) equals or exceeds Triskelion's toughness (3), so it would already be destroyed as a state-based action from point 0 (C.R. 704.5g).
Then the key to us (me and my buddy/opponent) understanding this problem is: 1) when are state-based actions checked during this process and 2) what is considered the state of the Triskelion when this happens?
For instance: Are state-based actions checked when a counter is removed to activate the ability? If so, is Triskelion considered with its new power/toughness minus a counter, or with its old power/toughness since nothing has yet resolved?
Are state-based actions checked when my opponent passes to me, and what is (if Triskelion is still alive) which power/toughness is considered?
When a step/phase begins, SBAs are checked, then triggers go on the stack, then the active player gets priority.
The active player gets priority after a spell or ability resolved. So right before that, SBAs are checked.
The player who activated an ability, cast a spell, or took a special action, gets priority afterwards. Before that, SBAs are checked.
During the cleanup step SBAs are checked.
In the case of this combo, SBAs are checked right after the activation of Triskelion's ability (so after the counter is removed, since that is a cost), and after its ablity resolved.
SBAs always use the current power/toughness of the creature. If you remove a +1/+1 counter, both drop immediately by -1/-1.
EDIT (Jan. 15): Clarification.
EDIT (Apr. 5): Added rule citation.
EDIT (May 16): Edited post to conform to "put" rather than "place" convention introduced in Amonkhet.
0. Assume 3/3 Triskelion with 3 damage marked (1/1 naturally, +1 from Mikaeus, +1 counter.)
1. Opponent removes final counter to activate Triskelion, passes priority.
2. I activate ability to add 1 counter to Triskelion, pass priority. Opponent cannot yet remove this counter, because it hasn't resolved.
3. Both players have passed, first ability on stack resolves: Triskelion gets a +1/+1 counter and is again a 3/3 with 3 damage marked.
4. Opponent would receive priority, (116.3b) but first state-based actions are checked (704.3) and Triskelion dies (704.5g) and goes to the Graveyard before
opponent receives priority.
5. Undying tries to trigger (603.4) and fails because Triskelion had a +1/+1 counter when it last existed (either during Step 3 or all the way back in Step 0). Combo is disrupted.
BUT I could be misinterpreting the rules. Can somebody check my math?
This is already wrong. A 3/3 with 3 damage marked will be desroyed by state based actions before any player can do anything. So if this occurs, the Triskelion will not come back.
The combo works by making Triskelion shoot itself twice with its last two counters. This way, there is a 2/2 Triskelion with no counters on the field and it eventually will have two damage marked, destroying it, and triggering undying. If you somehow place another counter before Triskelion dies, your opponent can simply remove it to deal damage to something, or target Triskelion itself. More +1/+1 counters are just more fuel for the fire.
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 (Jan. 15, 2018): Correct rule citation.
For instance: Are state-based actions checked when a counter is removed to activate the ability? If so, is Triskelion considered with its new power/toughness minus a counter, or with its old power/toughness since nothing has yet resolved?
Are state-based actions checked when my opponent passes to me, and what is (if Triskelion is still alive) which power/toughness is considered?
The active player gets priority after a spell or ability resolved. So right before that, SBAs are checked.
The player who activated an ability, cast a spell, or took a special action, gets priority afterwards. Before that, SBAs are checked.
During the cleanup step SBAs are checked.
In the case of this combo, SBAs are checked right after the activation of Triskelion's ability (so after the counter is removed, since that is a cost), and after its ablity resolved.
SBAs always use the current power/toughness of the creature. If you remove a +1/+1 counter, both drop immediately by -1/-1.
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)