Surge Mare

A 0/5 that would rather bleed you for cards than sit still. The base body stonewalls ground aggression, but the activation rewrites it into a 2/3 attacker, and it slips past any green creature trying to block, so the wall built to absorb attacks becomes a repeatable clock. Because the +2/-2 wears off at cleanup, the toughness snaps back to five before the opponent ever gets a swing: the mare returns to defensive size the moment the turn passes, so it can attack as a 2/3 (or a 4/1, at two activations) again and again without ever killing itself. The connection trigger loots you a card deeper each time it gets through, which is what makes paying to attack worthwhile. The pump is not a one-shot push but the fee for converting combat damage into filtering and graveyard fuel. The discipline lives in the arithmetic of the ability, not in any self-destruct timer: each activation raises the offense while gutting the defense for exactly one combat, so every attack is a live choice between holding the wall and cashing toughness for pressure and selection. Play defense while the ground is stalled; spend the body when a window opens; reset and do it again. The Horse Fish typing is a curio, but underneath sits a tidy tension between a permanent that wants to block and an activated ability that pays you, in cards, to stop blocking.