Expendable Troops

The body is the bait; the ability is the trade. What's on offer is a soldier that walks into combat looking like ordinary aggression, then converts itself into a removal spell the instant the math turns bad. The activation is the whole pitch: tap and sacrifice to deal 2 damage, but only to a creature that has committed to combat. That restriction is what holds the rate in check. It cannot snipe a mana dork on the draw step or pick off a fresh threat before it attacks; it waits for a creature to declare itself an attacker or blocker, then punishes the commitment. Functionally it lets a 2/1 trade with something that should outclass it, while the body still gets to swing on the turns combat goes your way. The sacrifice clause also means removing the Troops in response won't stop the ability: there is no creature left to kill once it's on the stack, so the 2 points still resolve even if an opponent tries to answer the body. That is the quiet appeal of a sacrifice-to-effect creature over a comparable instant. It carries a permanent's worth of board presence until the moment you decide it is worth more dead, and it picks that moment at instant speed inside the combat step, where most defensive tools cannot interfere.