Your bishops can only ever retreat toward your own back rank; they can never advance and never even hold their rank.
Retreating 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.
“The clergy only ever falls back.”