Ichorclaw Myr

The blocking trigger is the whole bet, and it inverts the basic problem of an infect creature. A 1/1 with infect is terrifying when it swings into an open board, where every point of combat damage becomes a poison counter, but it's useless once an opponent puts any body in front of it: a single blocker trades into the 1/1, and the clock stalls. This one punishes the trade. Become blocked and the body swells to a 3/3 for the turn, so the blocker now has to survive three -1/-1 counters rather than one. A 1-toughness chump still dies and absorbs the swing, but anything the defender wanted to keep around had better have four toughness to walk away intact. The asymmetry is the design: it costs the attacker nothing to find out, while the defender has to commit a creature that's actually big enough to survive being shrunk, or watch a cheap blocker get vaporized. That makes it a wedge against the natural defense to poison, which is to gum up the ground with disposable bodies and absorb the attacks. The wrinkle is that the pump only fires on being blocked, so it does nothing to force poison through an empty board; the card wants the opponent to believe blocking is safe, then taxes the instinct. A modest body wearing infect and a trap, built so that the correct read against it is rarely the comfortable one.