Flameskull

The 3/1 flyer that can't block is an aggressive body priced for tempo, but the Rejuvenation trigger is where the real accounting happens: this thing was built never to be a true two-for-one against your opponent, only a two-for-one against attrition. When it dies it exiles itself and the top card of your library, then hands you a window that stretches into your next turn to play one of them. The clause that keeps the whole design from spiraling is the exclusivity: cast Flameskull off the exile and you forfeit the extra card; play the extra card and the skull stays gone. So the card doesn't generate advantage so much as refuse to be traded away, converting every removal spell into a stalling tactic rather than a clean answer. It's a recursion design that lives in the space between a body and a cantrip, useful precisely because opponents can't decide which half they're spending resources to stop. The can't-block rider does the balancing: forbidding defense keeps this from being a blocker you recur forever, and points the whole package back at a life total where the tempo math is meant to live.