Scandinavian Variation (2.Nc3 d5)

The idea

After 2.Nc3 d5 3.exd5 Nxd5, the position resembles a Scandinavian, with Black's knight on d5. Wikipedia calls 2...d5 the independent Alekhine line and notes that after 4.Bc4, 4...Nb6 or 4...Nxc3 is considered roughly equal.

Plans for White

Develop with Bc4, Nf3 and castling, or g3 and Bg2. White can also play the more combative 3.e5. Jonny Hector regularly plays 2.Nc3 and has scored well against 2...d5, and Wikipedia says his ideas have left White with a theoretical edge.

Plans for Black

Trade on c3 or retreat to b6, then develop with ...e6 or ...Bf5 and ...Nc6. 4...e6 is solid but blocks in the light-squared bishop, Wikipedia notes. Black's game is simple and sound.

Watch out for

For Black, being out-prepared. Textbook authors such as Davies, Cox and Taylor have encouraged 2...e5 instead of 2...d5 because of White's recent ideas.

For White, bluffing. John Cox writes that many White players who play 2.Nc3 know little about the Vienna or Four Knights it can transpose into, so after 2...e5 they need to know those openings.