A zombie horde bites pieces and turns them into zombies.
How to play
Standard armies and check rules (no castling or en passant): you may not leave your king in check, checkmate wins and stalemate is a draw. A green zombie knight starts in the centre. After every round, the horde moves one zombie: if it can attack a living piece of either colour, it bites it and that piece turns into a zombie of the same type (a bitten king dies). Zombies belong to nobody, and you or Black can destroy them by capturing them. Zombies ignore check, and the horde never uncovers an attack on Black's king. A side whose king is bitten, or which has no living pieces left besides its king while zombies roam, loses.