The Green Knight

An immortal green knight in the centre feasts every round, alternating between hunting White and Black.

A green knight stands at the centre of the board and cannot be captured. It plays once per round. It is always hungry. It eats one of White's pieces one round, one of Black's the next, and so on. If it can reach a piece of the colour it is hunting, it takes the most valuable one it can. If it cannot, it stalks one knight-hop closer to that colour and refuses to touch the other side, unless every square it could jump to is occupied by them, in which case it is forced to feed. It eats kings last of all, but it does eat them: let the Green Knight take your king and you lose.