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-MadMage
Can an opponent target the creature that gets sacd to Contamination on the trigger resolution? Is the sacrifice a cost?
I sac Reassembling Skeleton on the resolution, my opponent can't Path To Exile in response, right?
They can't cast or activate anything in the middle of Contamination's resolution.
608.2g If an effect gives a player the option to pay mana, they may activate mana abilities before
taking that action. If an effect specifically instructs or allows a player to cast a spell during
resolution, they do so by following the steps in rules 601.2a–i, except no player receives priority
after it’s cast. That spell becomes the topmost object on the stack, and the currently resolving
spell or ability continues to resolve, which may include casting other spells this way. No other
spells can normally be cast and no other abilities can normally be activated during resolution.
405.6. Some things that happen during the game don’t use the stack.
405.6a Effects don’t go on the stack; they’re the result of spells and abilities resolving. Effects may
create delayed triggered abilities, however, and these may go on the stack when they trigger (see
rule 603.7).
They can respond to the Contamination trigger itself and target something that they think you are going to choose for the sacrifice, but you would still have a free choice of your (remaining) creatures once the Contamination trigger resolves.
The sequence would probably be one of the following:
Your upkeep begins. The ability of Contamination triggers.
You would get priority, but there is a triggered ability to put on the stack. You put "At the beginning of your upkeep, sacrifice Contamination unless you sacrifice a creature." on the stack.
You get priority and pass.
Opponent gets priority and passes.
The top object on the stack (the ability put there in step 2) resolves. You choose to sacrifice Reassembling Skeleton, putting it in your graveyard.
You get priority and ....
Your upkeep begins. The ability of Contamination triggers.
You would get priority, but there is a triggered ability to put on the stack. You put "At the beginning of your upkeep, sacrifice Contamination unless you sacrifice a creature." on the stack.
You get priority and pass.
Opponent gets priority and casts Path to Exile. They guess that you are going to need Reassembling Skeleton in a moment, so they choose that as the target. They pay the cost using W obtained in an unspecified way (but probably not by tapping a land).
Opponent gets priority and passes.
You get priority and pass.
The top object on the stack (the spell cast in step 4) resolves. Opponent exiles your Reassembling Skeleton. You may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle. (I don't know what your actual decision would be.) The spell is put in opponent's graveyard.
You get priority and pass.
Opponent gets priority and passes.
The top object on the stack (the ability put there in step 2) resolves. You have the option to sacrifice one of your remaining creatures. If you do, the resolution is done. If you don't, you sacrifice Contamination.
I sac Reassembling Skeleton on the resolution, my opponent can't Path To Exile in response, right?
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-MadMage
[c]Reassembling Skeleton[/c] -> Reassembling Skeleton
[c]Path to Exile[/c] -> Path to Exile
They can't cast or activate anything in the middle of Contamination's resolution.
They can respond to the Contamination trigger itself and target something that they think you are going to choose for the sacrifice, but you would still have a free choice of your (remaining) creatures once the Contamination trigger resolves.
The sequence would probably be one of the following: