Bishop's opening - MacDonnell double gambit
1. e4 e5 2. Bc4 Bc5 3. b4 Bxb4 4. f4
White pushes the king's pawn to e4. Black plays the king's pawn to e5. White develops the light-squared bishop to c4.
Black develops the dark-squared bishop to c5. White advances the b-pawn to b4. Black captures with the dark-squared bishop on b4.
White pushes the f-pawn to f4.