Castling, en passant and promotion

It is the only move in which two pieces move: the king moves two squares towards a rook and that rook jumps to the other side of the king. It protects the king and activates the rook.

Requirements: neither the king nor that rook has moved before; there are no pieces between them; the king is not in check, and it does not pass through or land on an attacked square. On the board, drag the king two squares towards the rook.

If a pawn advances two squares and ends up right next to an enemy pawn, that enemy pawn can capture it as if it had moved only one square. It can only be done on the very next move.

A pawn that reaches the last rank turns into a queen, rook, bishop or knight. A queen is almost always the choice.