Xathrid Slyblade

The clever knot here is that the protection and the threat can't coexist. Hexproof keeps the Slyblade untouchable while it sits back, but the instant you want it to win a fight (first strike to land damage uncontested, deathtouch to make any block fatal) you pay and it sheds the cloak, becoming targetable until the turn ends. That window is the whole design: an opponent holding a kill spell waits for you to flip the switch, then answers the now-vulnerable body before it connects, or you commit while they're tapped out and the assassin does its work. The 2/1 frame sharpens the tension. Left hexproof, it's a safe but toothless body, since neither first strike nor deathtouch is online until the toggle flips. The moment it gains the keywords that let a 2/1 trade up against anything, it also hands the opponent a target it never had before. So the activation isn't just a mana sink; it's a deliberate exposure. The card plays like a bluff war over a single button: the combat upside it threatens is paid for in the protection it gives up, and the read is whether your opponent can punish that gap before damage resolves.