Revoke Demise

If the target creature card is an illegal target as Revoke Demise tries to resolve, it won't resolve and none of its effects will happen. You won't gain life.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.