HYDRA is a card game for 2-6 players, but at its core designed for 4 players. In this game, the order determines who attacks and who defends. As the attacker, you take on the role of the Hydra and try to successfully carry out your attacks and bring home your points (stake). You do this by getting rid of your hand cards before anyone else. The other players try to prevent this or "secretly" support the attacker.
But the whole thing comes with a twist in two ways! On one hand, each player plays for him/herself, but is always part of one of two teams. On the other hand, there are the ever-changing teams, which are determined by the COMPANION CARD and can also change during the game. Phew! Are you still keeping track of who your real team members are, or are you being cheated through your teeth?
—description from the publisher (translated)