Castling
Castling is the only move in chess that moves two of your pieces at once: the king goes two squares toward a rook, and the rook lands on the square the king passed over. It tucks the king away from the open central files and activates the rook in a single tempo. Neither piece may have moved before, the squares between them must be empty, and the king may not castle while in check, through an attacked square, or into check.
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8.
Two pieces move at once: the king to g1 and the rook to f1 — the only such move in chess.