Oko, Thief of Crowns

Oracle Text
+2: Create a Food Token
+1: Target artifact or creature loses all abilities and becomes a green Elk creature with base power and toughness 3/3
-5: Exchange control of target artifact or creature you control and target creature an opponent controls with power 3 or less.
The +1 is solid in a normal 60-card game, but a 3/3 means almost nothing in commander; He's free repeatable removal that also Mutates commanders.
And he also crushes it in drafts by coming down way too early. gaining you life, and turning all your dudes to 3/3s
But once you get to where a 3/3 is no threat, oh boy. Direct damage won't take him out easily. You can stall and steal everything if your own stompy creatures aren't enough. This is the sort of card that makes people quit the game.