+1: Until end of turn, target creature can't block.
-3: Gain control of target creature until end of turn. Untap that creature. It gains haste until end of turn.
-7: You gain an emblem with "Whenever an activated ability other than a mana ability is activated, you may copy that ability. You may choose new targets for the copy."
Originally I wanted to make the first ability something that made the next spell your opponent cast that targeted a creature hit a random creature instead, but I couldn't find a reasonable-sized wording for that ability.
I also considered this walker at 5cmc starting loyalty 5 and the ultimate costing 8.