Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast a noncreature spell, you may pay. If you do, target creature gains double strike until end of turn.
11/24/2014 Any spell you cast that doesn’t have the type creature will cause prowess to trigger. If a spell has multiple types, and one of those types is creature (such as an artifact creature), casting it won’t cause prowess to trigger. Playing a land also won’t cause prowess to trigger.
11/24/2014 Prowess triggers only once for any spell, even if that spell has multiple types.
11/24/2014 Prowess goes on the stack on top of the spell that caused it to trigger. It will resolve before that spell.
11/24/2014 Once it triggers, prowess isn’t connected to the spell that caused it to trigger. If that spell is countered, prowess will still resolve.