Witchstalker | Magic: The Gathering
Formats Witchstalker is Legal in
Official Oracle Text for Witchstalker
Whenever an opponent casts a blue or black spell during your turn, put a +1/+1 counter on Witchstalker.
Official Rulings for Witchstalker
7/1/2013 : If an opponent casts a copy of a card that’s blue or black during your turn (as opposed to putting a copy of such a spell directly on the stack), the ability will also trigger. Check for the word “cast” in the effect that creates the copy.