The KGD with 2...Nf6 arises after 1.e4 e5 2.f4 Nf6. ECO code: C30.

Black develops the knight and attacks e4, a logical declining response. After 3.fxe5 Nxe4 or 3.Nc3, the position can become sharp. The move is flexible and avoids the main-line gambit complications.