Muzio Gambit, Wild Muzio Gambit

With 5. O-O, White ignores the attacked knight on f3 and castles, so that the f1-rook joins the attack at once. Black almost always takes the piece with 5...gxf3, and after 6. Qxf3 the queen, rook and c4-bishop all bear on f7 while Black's kingside is undeveloped and the f4-pawn is a target. The usual defenses are 6...Qf6 and 6...Qe7. The sharpest try is the Double Muzio, 6...Qf6 7. e5 Qxe5 8. Bxf7+, in which White is two pieces down after eight moves, yet some masters regard the position as equal. Black can also decline the knight for now. The Brentano Defense, 5...d5, returns a pawn to slow White before taking on f3, and the Kling and Horwitz Counterattack is 5...Qe7.

Compared with the related 5. d4 (Ghulam Kassim Gambit) and 5. Nc3 (McDonnell Gambit), castling is considered stronger because it adds the rook to the f-file pressure. Engines give Black a clear advantage, but accurate defense is required. In online games White scores well, and the line works best against an unprepared opponent.