Fog Elemental

Four power on an evasive body for three mana is a rate that should not exist, and the second line is precisely why it survived a design review: the elemental sacrifices itself at end of combat the instant it commits to attacking or blocking. That clause turns the front-end numbers into a one-shot. Swing with it through an open sky and it lands four in the air, exactly once, a body you spend rather than develop. Throw it in front of a swinging attacker and it trades up (it can soak a much larger creature and, if that creature's toughness is four or less, kill it, then vanish on its own and leave the board clean). The self-destruct only fires on its own attack or block, never on merely existing, which opens a quieter mode: held back, the elemental sits in play indefinitely as a four-toughness flying deterrent an opponent has to plan around without it ever being spent. The whole tension lives in choosing the moment to cash it in. Commit on the convenient turn and you have wasted a permanent-looking threat on a single exchange; commit on the right one and the rate pays for the impermanence. It is a creature designed to be a verb rather than a noun: a one-time effect wearing a flyer's stat line, used once and replaced rather than protected and grown.