Marchesa's Emissary

Two keywords pulling in the same direction, which is rarer than it sounds. Dethrone wants this swinging into the table's life-total leader, and its counter is a triggered ability: declaring the attack puts the trigger on the stack, and once it resolves the creature grows whether or not the swing ever connects. Hexproof narrows the answers rather than removing them. It shuts off targeted spot removal, the cleanest response to a creature that snowballs in combat, but it does nothing against a chump blocker thrown under it, a board wipe, or an edict that makes you sacrifice. The 2/2 body is the tax: this starts small and asks you to let it attack a few times before it earns its keep, the natural counterweight to a counter-accumulating threat that can't be picked off with a burn spell. And the growth only insulates it from one narrow class of answer: pile enough counters and a Pyroclasm-style damage sweeper or an -X/-X effect stops reaching it, but a Wrath of God does not care how large it has gotten. The result is a piece built for free-for-all politics, where the life leaderboard shifts often enough to keep feeding the trigger. Dethrone rewards attacking the leader or anyone tied for it, so even in a duel where you and your opponent sit level on life the counter still lands; only once you pull ahead does the incentive to attack go quiet, right when you would most want the growth to continue.