Chess Opening Theory/1. e4/1...c6/2. d4/2...d5/3. Nc3/3...dxe4/4. Nxe4/4...f6/5. Ng3

=Caro-Kann f6=

This refutes the f6 line.

Epilogue
Ng3 is an interesting but important move that allows the e5 pawn push, but gains a huge lead in development after '''5...e5 6. Nf3'''.