Hmm, do you mean
http://de.lichess.org/forum/off-topic-discussion/cats#10?
But for what are the cat pieces needed then?
How about:
* three players, white starts, then black, then cat player, then white again etc.
* Cat player has one cat, it is not placed on the board in start position.
* Cat can go everywhere, eg cat a8-g1 or cat d4-d3 are legal moves.
* But there must be a 'hole' to reach target square. hole is defined as: reachable by any standard piece placed anywhere. eg if in start position ra1 would be placed on b3 then cat could not go to a1. But if rook would be placed on a3, then cat could (because a nb3 could go to a1).
* cat can also go off the board and back.
* cat can be taken like a normal piece.
* cat can block but not take pieces.
* When it is cat players move he can but does not have to make a move.
* if cat has a piece on one of the 8 squares around it it can also move that piece (must be a legal move for that piece). Counts as a cat move.
* Cat player wins when the Game is draw. He loses if the cat gets lost or if white or black wins.