Escaped Null

Combat is where the trap springs. A 1/2 with lifelink reads as harmless until the instant a creature is declared as a blocker or becomes blocked, at which point the +5/+0 turns it into a 6/2 with lifelink until end of turn. That conditional is the entire engine: the bonus pays out only at the moment of commitment in combat, never while the creature sits idle. Sent in, it forces a choice on your opponent: block and eat six (and hand you six life through lifelink), or let it through for a single point and refuse to feed the trick. On defense it runs the same squeeze from the other side, killing most attackers that walk into it while gaining you six, or sitting home if the attacker routes around. The toughness staying at 2 is what keeps the design in check: the bonus is pure power, so the 6/2 trades down to most of what it kills and dies to any burn of two or more aimed in response, which prevents a four-mana common from spiraling out of control. The lifelink is what converts each of those combat coin-flips into a real life swing, since every point of the temporary six counts. This is a tempo-and-attrition design built on a single principle: combat math only changes once a creature is committed, and a clever attacker or blocker can make that commitment hurt either way.