Mana-Charged Dragon
Join forces is one of multiplayer Magic's most openly chaotic mechanics: it hands an effect to the whole table and asks everyone to bid into it, and the bidding is where the politics live. Most join-forces cards spread their payoff evenly, which makes them feel communal. This Dragon does the opposite. It is a 5/5 flier with trample that grows by the total mana every player pours in, but only its controller decides who it swings at. So when the table pays to pump it, they are funding an attack they do not aim. The result is a strange, self-defeating negotiation: opponents who refuse to pay let the Dragon stay small, opponents who pay turn it into a one-shot kill that points wherever its controller likes, and the controller's own mana sets the floor. Trample is the line that makes the bidding lethal rather than theoretical, because the +X/+0 buys raw face damage that a single chump block cannot soak up. In practice the card weaponizes the social contract of join forces against the players who buy into it, which is a sharper design idea than the splashy "everyone contributes" framing suggests. It rewards a politician at the table far more than a deckbuilder, since the real engine is convincing the player to your left that feeding the Dragon hurts someone else first.
