Your bishops can't retreat on a quiet move, but they may still strike backward: a bishop may only lose rank when the move is a capture.
One Way Bishopsis one of Nerf Chess's secret handicaps. In Nerf mode you choose one of two nerfs before the first move, in secret, and carry it for the whole game.
The board quietly enforces it: any move it forbids is simply never offered, so you cannot break it by accident. Your opponent never sees which nerf you took until the game ends, so every move you make is also a clue they are trying to read.
“Faith advances, and draws blood where it must.”