It’s like chess, but you have a hidden drawback! You can’t see your opponent’s drawback, and they can’t see yours. The drawbacks are enforced by the game. You won’t be able to make illegal moves, and your legal moves will be highlighted for you if you click on or pick up a piece.
Checkmate and stalemate do not exist. You lose if your king is captured or if you have no legal moves (due to your drawback). It is legal to ignore apparent threats to your king, move into check, move a piece that’s pinned to your king, etc.