The Blackburne Shilling Gambit (Blackburne's Shilling Gambit) starts out 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4!? which may be considered dubious among masters but interesting among the rest of the world. Normal for Black is a Giuoco Piano with 3...Bc5 and a Two Knights Defense with 3...Nf6. The Encyclopedia of Chess Openings (ECO) designation is C50, but not really covered in ECO (too amateurish). Graham Burgess calls 3...Nd4 the "Oh My God" trap. 3...Nd4 is sometimes known as the Kostic Gambit, named after the Serbian grandmaster who played it in the early part of the 20th century.
The name seems to have caught on because Joseph Henry Blackburne (1841-1924), Mr. Black Death, would play any amateur for one shilling (G. Chandler likes to call it the 5 pence metric trap) and he would usually play this opening and win. The trap wouldn't work for masters, but it was a source of income for Blackburne against amateurs unfamiliar with the trap. But did Blackburne really play this? There are no games of his with this trap. The name seems to first appear in the 2nd edition of The Oxford Companion to Chess by Hooper and Whyld, page 43, published in 1992.
White's mistake is to take the e-pawn with 4.Nxe5. Better is to leave the pawn alone and castle with 4.O-O or just play 4.Nxd4 exd4 5.O-O or 5.Qf3. Another idea is 4.c3.
The main trap is 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxe5 Qg5 5.Nxf7?? Qxg2 6.Rf1 Qxe4 7.Be2 Nf3 mate 0-1. This is the Blackburne Shilling mate. The first known game with all these moves is Muhlock-Kostic, Cologne 1912. It was repeated in A. Jordan - Newell Banks, USA 1917. These same moves were mentioned by William Steinitz in the Modern Chess Instructor.
6.Nxh8 doesn't work.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxe5 Qg5 5.Nxf7?? Qxg2 6.Nxh8 Qxh1+ 7.Bf1 Qxe4+ 8.Be2 d5 9.d3 Nf3+ 10.Kf1 Bh3 mate 0-1 Mueller-Pieper, Eppingen 1988
6.Qh5 doesn't work
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxe5 Qg5 5.Nxf7?? Qxg2 6.Qh5 Qxh1+ 7.Bf1 Qxe4+ 8.Be2 g6 9.Qg4 Qxg4 10.Bxg4 Kxf7 wins for Black Kramer-Wall, Washington State 1969
Another bad idea is to play 5.Ng4.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxe5 Qg5 5.Ng4? d5! 6.Bxd5 Bxg4 (6...Qxg4 7.Qxg4 Bxg4 8.Bb3 Be7 Leite-Benaissa, Bratislava 1993) 7.f3 Bxf3 8.gxf3 Qg2 9.Bxf7+ Kxf7 10.d3 Qxh1+ 11.Kd2 Nxf3+ 12.Ke2 Qxd1+ (or 12...Nd4+!) 13.Kxd1 Nxh2 14.Bf4 Ng4 White resigns 0-1 NN - C. Gold, England 1979
Another bad idea is 5.c3
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxe5 Qg5 5.c3? Qxg2 6.Rf1 Qxe4+ 7.Be2 Nc2+ (8.Qxc2 Qxc2) 0-1 Kozelek - Holzmann, Germany 1929
Another bad idea is 5.Nd3
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxe5 Qg5 5.Nd3? Qxg2 6.Rf1 Qxe4+ 7.Qe2 Qxe2 mate 0-1 Choate - Moceri, Detroit 1994
Better for White is to play 5.Bxf7+ instead of 5.Nxf7.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxe5 Qg5 5.Bxf7+ Ke7 (5...Kd8) 6.O-O Qxe5 7.Bxg8 Rxg8 8.c3 Nc6 9.d4 Qa5 (9...Qf6) 10.d5 Ne5? 11.Qh5 Nf7?? (11...h6) 12.d6 (and 13.Qxe5) 1-0 G. Chandler - NN, Stockbridge 1983
White should avoid taking Black's e5 pawn and try something else, such as 4.Nxd4.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxd4 exd4 5.c3 dxc3 6.Nxc3 Qg5 7.d3 (7.O-O) 7...Qxg2 8.Rf1 Bb4 9.Qb3 (9.Qh5; 9.Bf4) 9...Bxc3+ 10.bxc3 (10.Qxc3) 10...Qg6 11.Bf4 (11.Be3) 11...c6 12.O-O-O? (12.a4) 12...b5 13.Rg1 bxc4 14.Qxc4 Qf6 0-1 Wall-Aker, Correspondence 1981
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxd4 exd4 5.c3 Qe7 6.O-O dxc3 7.Nxc3 c6 8.d4 Qd8 9.Qh5 Qe7 10.e5 g6 11.Qf3 Bg7 12.Bg5 Qf8 13.Ne4 d5 14.Nd6+ Kd7 15.Nxf7 (15.Bd3) Wall-Upton, Internet 1996
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxd4 exd4 5.Qf3 Nf6 6.d3 c6 7.Bg5 Be7 8.Nd2 O-O 9.O-O-O Qa5 10.Bxf6 Bxf6 11.Kb1 Rd8 12.h4 d5 13.Nb3 dxe4 14.Qxf6 Qf5 15.Qxd8 mate 1-0 Montgomery-Randall, Ohio 1980
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxd4 exd4 5.O-O g6 6.d3 Bg7 7.c3 Ne7 8.cxd4 Bxd4 9.Nc3 c6 10.Bh6 d5 11.exd5 cxd5 12.Bxd5 Nxd5 13.Qa4+ Bd7 14.Rfe1 Ne7 15.Qxd4 Rg8 16.Nd5 Be6 17.Nf6 mate 1-0 Bradshaw-Brown, Liverpool 1974
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxd4 exd4 5.d3 c6 6.Qf3 Nf6 7.e5 Qa5+ 8.Kd1 d5 9.exd6 Bg4 0-1 Xing-Wall, Internet 2004
Another idea is 4.O-O
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.O-O b5!? (4...Nxf3+) 5.Bxf7+ (5.Bb3) 5...Kxf7 6.Nxe5+ (6.Nxd4) 6...Ke7 7.c3 d6 8.Qh5? (8.cxd4) 8...dxe5 9.Qxe5+ Ne6 10.d4 Qd6 11.Qxd6+ cxd6 12.f4 Bb7 0-1 Rub-Wall, Palo Alto 1989
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.O-O Nxf3+ 5.Qxf3 Qf6 6.Qg3 (6.Qc3 Ne7 7.f4 exf4 8.Qxf6 gxf6 9.Rxf4 Bg7 10.Nc3 Rg8 11.Nb5 Kf8 12.Nxc7 Rb8 13.d4 d6 14.Nb5 Nc6 15.c3 a6 16.Nxd6 1-0 Wall-Deaky, Internet 1997) Bc5 7.Nc3 c6 8.Kh1 b5 9.Bb3 d6 10.f4 h5 11.d3 Be6 12.f5 h4 13.Qg4 Bxb3 14.Bg5 Nh6 15.Qxh4 O-O-O 16.Bxf6 gxf6 17.axb3 Nxf5 18.Qxh8 Ng3+ 19.hxg3 Rxh8 mate 0-1 J. Dunlop - E. Hicks, New Zealand 1911 (perhaps the earlies game with this opening).
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.O-O Nxf3+ 5.Qxf3 Nf6 6.Qb3 Qe7 7.Nc3 c6 8.a4 g6 9.d3 Bg7 10.f4 exf4 11.Bxf4 O-O 12.Rf3 d6 13.Raf1 Be6 14.Bg5 Bxc4? (14...d5) 15.Qxc4 d5 16.exd5 cxd5 17.Nxd5 Qd6 18.Bxf6 1-0 Wall-Kaya, Internet 1998
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.O-O d6 5.Nxd4 exd4 6.Qh5 g6 7.Qd5 Nf6?? (7...Qf6) 8.Qxf7 mate 1-0 Wall-McCoy, Internet 2002
Another idea is 4.c3
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.c3 Nxf3+ (4...b5 5.Bxf7+ Kxf7 6.Nxe5+ Ke7 7.cxd4 d5 8.Nc6+ 1-0 Wall-Andre, Internet 2000) 5.Qxf3 Qf6 6.Qe3 Qf4 (6...Ne7 7.O-O c6 8.f4 Ng6 9.fxe5 Qxe5 10.Bxf7+ Kd8 11.d4 Qe7 12.Qg3 1-0 Wall-Amuary, Internet 1999) 7.Qxf4 exf4 8.d4 Nf6 9.Bxf4 c6 10.e5 Nd5 11.Bxd5 cxd5 12.Nd2 Be7 13.Nf3 h6 14.b3 g5 15.Bg3 b5 16.h4 gxh4 17.Nxh4 Bxh4 18.Bxh4 d6 19.exd6 O-O 20.Be7 Rfe8 21.Rxh6 Be6 22.Bf6 1-0 Wall-Zeppelin, Internet 1999