karn, war general

+2: search your library for a colorless artifact card and put it in your hand. when you cast it, cast it for half its converted mana cost, rounded up
-4: until end of turn, karn becomes a 5/5 golem creature with infect and indestructible. it's still a planeswalker
-12: create X 0/0 constructs, where X is the number of artifacts you control. they have "this creature gets +1/+1 for each artifact you control."