Cannon at the bottom of the sea
海底捞月 — scooping the moon from the sea — is the classic kill in chariot-and-cannon endgames. The general anchors the centre file, and the cannon sinks to the very bottom on the king's own file — here d0 — firing through Black's guard rook on d7. That rook is helpless: capturing the mating chariot would only make it the cannon's new screen. The king cannot step to e9, because Red's general glares up the open centre, and the palace wall bars c9 forever. Scoop the moon: crash the chariot onto the advisor at d8, the last barrier.