1.Nf3 f6 2.Nd4 Nh6 3.e3 Ng4 4.f4

Black can try:

4...c6 (maybe losing),

4...b5,

4...d5,

4...Nf2,

4...Na6 5.Nb5 (or 5.Nf5 e5) Nb4,

4...e5 5.Nb5 Bb4 6.c3 c6 7.Nxa7.