ProwessProwess is a triggered ability. “Prowess” means “Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.”
If a creature has multiple instances of prowess, each triggers separately. (CR 702.108) (Whenever you
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) a noncreature spell, this creature gets +1/+1 until end of turn.)
When this creature enters, you get
(three
energy countersA counter on a player that remains until spent or removed. (CR 122.1b)).
When this creature
diesIs put into a graveyard from the battlefield. (CR 700.4), you may pay
. When you do, this creature deals damage equal to its power to any target.