Scotch Game, main line 
A common line of the Scotch Game, Bc5 attacks the d4 knight and puts indirect pressure on the f2 square if the knight moves.
White's standard response is to support the d4 knight with 5.Be3, which threatens to immediately win a piece with Nxc6, dxc6(...Bxe3; Nxd8 wins the black queen); Bxc5. Play will often continue 5...Qf6 6.c3, and is thought to be equal for black.
Other playable moves all involve avoiding the committing of attackers and defenders against the d4 knight. These moves include 5.Nxc6, 5.Nf5 and 5.Nb3.
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