Crenellated Wall

Most defensive walls protect themselves: a fat toughness sits in front of the attack and holds. This one externalizes the toughness instead, tapping to dump +0/+4 onto any creature for the turn. That changes what the card is doing on the battlefield. As a 0/4 with Defender it makes a fine blocker on its own, but its real function is as a repeatable combat-math distortion engine: a body you were never swinging with anyway, converted into the ability to ambush an attacker, save a blocker mid-combat, or push a creature out of burn range. The pump targets any creature, not just your own, which is mostly a rules quirk but occasionally a way to bait a trade. The design tension is the one every defensive utility piece has to negotiate: a body locked off offense has to earn its slot purely by what it denies the opponent, and a once-per-turn +4 toughness is a narrow, slow form of denial. It will not stop a swarm and it will not win a game; it asks to be the floor of a defensive shell rather than a payoff. The wall-as-toolbox idea runs through it cleanly: a creature that exists to feed an activated ability, with Defender pinning down exactly what role it is allowed to play.