1. d4 d5 2. Bf4 Nf6 Normal so far
3. Qd3 Moving out the big guns early
b6 Probably the wrong response. g6 was probably a better response allowing eventual Bc5, Bg7, Nc6 etc. lining up the bishops nicely to pressure the queenside long term
4. Qc3 Second queen move. Threatening the c7 pawn
Na6 protecting c7, there are other choices but they are more tactical
5. Qc6+ Third queen move forking king and unprotected rook
Bd7 Removes check, threatens the queen and discovers defense of the rook
6. Qb7 Fourth queen move. Threatens the knight but locks the queen deep in enemy territory with little support
Nb4 Traps the queen and threatens Nxc2+ forking king and rook
7. Bxc7 Bad idea, after the trade ( per text ) the bishop will be pinned to the c2 pawn and so is lost
Qc8 Pins the bishop to the c2 pawn and threatens whites hanging queen ( i.e. the queen trade is now forced )
8. Qxc8+ Rxc8 The queens have been traded and the bishop is still pinned to c2
9. Na3 protects c2
Rxc7 10. Nb5 Bad idea. Hangs the knight and removes the protection of c2
Nxc2+ Technically Bxb5 is simpler and stronger, but the text move traps the king in the centre. Forks king and rook
11. Kd2 Ne4+ The king only has three choices now. The text move, Kd1 ( Nxf2+ forking the king and the other rook ) and Kc1 ( Bxb5 with the discovered check still threatening one rook and Nxf2 threatening the other rook so at least one is lost )
12. Kd3 Bxb5# The protected knights make a nice box for the king and the bishop fills in the hole 0-1