Wave of Rats

A recursion loop that closes itself in the combat step: connect with a player, trade the body in a block or to a sacrifice outlet, and the death trigger walks it right back onto the battlefield. Everything hinges on that combat-damage clause. The return only fires if it hit a player this turn, so the card wants to be swinging into open air or through chump blockers, not sitting on defense. The 4/2 with trample is built for exactly that: big enough to shove damage past a single blocker, fragile enough that dying is the plan rather than an accident. Blitz is where the two halves start talking to each other. The alternate cost adds haste and a death-draw, but it also schedules its own sacrifice, and that sacrifice is not a downside so much as the fuse for everything else. Cast it via blitz, connect for damage, and when the forced sacrifice kills it, both the card draw and the return-to-battlefield clause fire off the same death. The sacrifice does not fight the recursion; it feeds it, converting a one-turn body into a card and a permanent that keeps coming back every time it lands a hit. Hard-cast for its normal cost, it is a straightforward attacker with a resilience clause; blitzed and connecting, it is a Rat that pays you to throw it away and then refuses to stay gone.