With this move, White punishes Black's weak move by taking the centre and tactically preventing e5. Black has wasted their chance to stop d4, so White happily plays it.

2...g5?? is the worst response, allowing immediate mate with 3. Qh5#. This is tied for fastest White checkmate with another mate, 1. e4 e5 2. Qh5 Ke7?? 3. Qxe5#.

2...Kf7?! is a joke continuation named the Fried Fox Defence^[1] where Black's king is exposed. After 3. Bc4+, White is clearly better as Black is unable to castle and behind in development.

2...e5 is the most common reply^[2]. However, after 3. dxe5, Black has simply lost a pawn as taking back with 3...fxe5?? would be absolutely disastrous due to 4. Qh5+! and White wins a rook after 4...g6 (4...Ke7 leads to Black having to sacrifice material to avoid mate after 5. Bc4+ d5 6. Bxd5+ Qxd5 7. Qxd5++-) 5. Qxe5+ Qe7 6. Qxh8+-, so 3...Nc6 instead is better, transposing into the Hammer Gambit (1. e4 Nc6 2. d4 e5 3. dxe5 f6!?) of the Nimzowitsch Defence^[3] where after 4. exf6 Nxf6 Black loses a pawn in exchange for quick development.

Other moves include:

2...g6 attempts not to fianchetto the bishop on g7, but to play Nh6-f7 without worrying about Bxh6 as Black would take back with Bxh6 and develop the bishop. After 3. Nf3 Nh6 Black scores quite well^[4].

2...e6 aims to develop the bishop and then place the g8-knight on e7 as f6 is blocked by the pawn. Although not as popular^[2], it is a relatively playable move to develop pieces.

2...Nc6 transposes to the Neo-Mongoloid Defence (1. e4 Nc6 2. d4 f6) of the Nimzowitsch Defence^[5] while developing the b8 queenside knight.