Schliemann gambit was thought to be refuted but it has recently seen a revival by Radjabov - he plays it to make a draw. We start with the game from Shirov where Black tries the weaker 7...Qd5. This game is very logical, and is easy to understand.
The critical line is 7...Qg5. Here we see a game between Karjakin and Radjabov.
Here is a game by Fisher.
Many times, Black will try 3...g6. The point is, if Black gets to play ...Bg7, then the bishop will control the d4 square, and make it hard for White to get his pawn to d4. So, White must play accurately, and disrupt Black's development.
And another try with 3...g6.
Next, there is the Bird's defense - that starts with 3...Nd4. Against it, the similar idea of playing Bc4 to put pressure on f7 is employed.
And a more decent try, but the same idea still works.
Black tries 3...Nge7.
Once again, White will reposition his bishop to c4 and play normally.
and another try with 3...Nge7 This one is explosive (highly tactical).
And in the end, there is the response 3...Bc5. A very positional approach with c3 and d4 is prescribed.