Halloween Gambit

White eliminates Black's central pawn, but gives up their knight to do so. The Hallowe'en gambit is an offbeat line where White sacrifices their knight so they can expand in the centre with tempo. The gambit is considered to be unsound and is uncommon in tournament chess, but it is tricky and aggressive and affords White lots of practical chances.

4...Nxe5, accepting the gambit, is almost always played and is the most critical line. Generally, Black can choose to either hold on to as much material as possible or return the material for a more straightforward game. After White plays 5. d4 with tempo, Black has the choice of where to retreat their knight: 5...Ng6 or 5...Nc6.

Declining the gambit is unusual. Black's choices are

• 4...Nxe4?!, recovering the pawn but declining White's offered knight. This is worse for Black after 5. Qh5, threatening Qxf7#, but 5. Nxc6 is also playable.
• 4...Bc5?! declines the knight and fails to recover the pawn, but transposes to a Stafford gambit after 5. Nxc6 dxc6.

4. Nxe5, also known as the Leipzig gambit, was described in the 1880s by Oskar Cordel as a favourite of the Leipzig chess club. Cordel said they knew it as the Müller-Schulze gambit, apparently not after any specific players but meaning an "everyman" opening (i.e. the Tom, Dick and Harry gambit).^[1]

The gambit received the name "the Hallowe'en attack" from Steffan Jakob, who revitalised it in the 1990s when he programmed a chess bot to develop an opening book around the line. Jakob likened the effect of the surprising gambit to the fright one experiences on seeing a Hallowe'en mask.^[2] Jakob had discovered the opening from the German-language magazine Randspringer; its author, Rainer Schlenker, had also described it in supernatural terms, saying the opening was "to wake up ghosts in the sleepy Four Knight's Game."^[1]

For explanation of theory tables, see theory table and for notation, see algebraic notation.
1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5

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Wikipedia has related information at Müller-Schulze Gambit

• Critical lines in the Halloween gambit - Paul Keiser (Unorthodox Chess Openings newsletter)