Refraction Trap

Refraction Trap doesn’t target the source of the damage it prevents. You choose that source as Refraction Trap resolves. If you cast Refraction Trap for {W}, the source you choose doesn’t have to be the red instant or sorcery spell an opponent cast.

If the chosen source would deal damage, Refraction Trap prevents 3 of that source’s damage and the source deals its excess damage (if any) at the same time. Immediately afterward, as part of that same prevention effect, Refraction Trap deals its damage. This happens before state-based actions are checked, and before the spell or ability that caused damage to be dealt resumes its resolution.

If the chosen source would simultaneously deal damage to multiple permanents you control, or would simultaneously deal damage to you and at least one permanent you control, you choose which of that damage to prevent. For example, if the chosen source is Earthquake, you might choose to prevent the next 2 damage it would deal to you and the next 1 damage it would deal to a creature you control. You don’t decide until the point at which the source would deal its damage.