Your king is made of glass: you lose the instant he is checked while standing beyond your own first two ranks. Kept at home, he can weather a check.
Glass Kingis 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.
“Safe in his chambers, shattered in the open.”