A variant built around the "Berolina pawn," invented by Edmund Nebermann in 1926, replacing every ordinary pawn. The king, queen, rooks, bishops, and knights all move as usual. Only the pawn is reversed: it advances diagonally (two squares from its starting rank), and captures one square straight ahead — the mirror image of an ordinary pawn. A small rule flip that quietly invalidates every opening you know.
Simplifications: en passant and castling are omitted. Check and checkmate aren't enforced — capturing the king directly ends the game.