Triggers can trigger at any time, but wait to go on the stack until a player would get priority.

I cast while you control . What happens? After a creature spell resolves, a player receives priority. But it’s not as simple as that. Before priority can be received, first the game has to check for state-based actions (SBAs) – things like creatures with lethal damage dying, or +1/+1 and -1/-1 counters canceling each other […]

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Can you respond to the choice of what to copy with Phantasmal Image? It depends!

This is a very common question with any kind of copy creature. The most important thing to note is that the static ability that lets you choose to copy something is NOT a triggered ability (if it was, pretty much every Clone-type creature would die for being 0/0 before you could choose to copy something!). […]

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