If a player plays Imperial Decree after dealing damage to a unit, does that unit die?
No, that unit will not die from Imperial Decree.
According to RiftJudge FAQ #8633 and #9561, Imperial Decree only creates a triggered ability that kills units that take damage after the card has resolved and its effect has become active. It does not look back in time to check for damage that occurred before the card was played.
Why it doesn't die:
- Event vs. State: The trigger condition for Imperial Decree is the event of "taking damage." If a unit was already damaged before the spell resolved, that damage event has already passed, so the condition is not met.
- No Retroactive Effect: Imperial Decree does not check the current state of damage on units; it only monitors for new damage events occurring while its effect is active.
Note: If that same unit were to take additional damage later in the same turn while Imperial Decree is active, the trigger would fire at that time and kill the unit.