2...Nc6
White again has the possibility of 3.f4, with a type of King's Gambit, or 3.g3. Most often, White plays 3.Bc4, when the solid 3...Nf6 transposes to the 2...Nf6 3.Bc4 Nc6 line. Weaker is 3.Bc4 Bc5, when 4.Qg4! is awkward to meet. 4...Kf8 and 4...g6 are thought the best moves, but neither is too appealing for Black. The natural 4...Qf6?? loses to 5.Nd5! Qxf2+ 6.Kd1, when White's king is in no real danger, and White has multiple threats: 7.Qxg7; 7.Nxc7+; and 7.Nh3 Qd4 8.d3 threatening to trap Black's queen with 9.c3.
Read more about this topic: Vienna Game