The Black Knights' Tango (1.d4 Nf6 2.c4 Nc6!?) is an offbeat but playable opening that many opponents aren't prepared for. GM Joel Benjamin wrote of it (in 2004, admittedly) "Opponents under 2200 tend to be a bit confused. They aren't programmed to meet this move; they can't pull something out of their repertoire." Best for White may be the restrained 3.Nf3 e6 (avoiding 4.Nc3 e5!) and now either 4.Nc3 Bb4 (transposing to a line of the Nimzo-Indian) or the prophylactic 4.a3, as Kasparov has played. My opponent in the game below played 3.d5, which IM Richard Palliser calls "The Lunge." White is probably thinking, "Let's blow this ridiculous opening off the board!," but it's not so easy. After 3...Ne5, he should have continued with the consistent 4.e4 e6 (4...Nxe4?? 5.Qd4) 5.f4 (or, more sedately, 5.Nf3, as Gligoric once played). Instead, he played the flaccid 4.b3?! e6 5.Bb2. After 5...Bb4+, he should have played 6.Bc3!, keeping a playable game. His 6.Nd2?? got crushed by 6...Ne4! 7.Bc1 Qf6! 8.Nf3 and now, while I was contemplating my next move, White resigned. I probably would have played 8...Ng4 followed by crashing in on f2, rather than 8...Nxf3+ 9.gxf3 (9.exf3? Nc3! 10.Qc2 Qe5+ is crushing) Qxa1 (9...Nxf2!?) 10.fxe4, when White could pretend that his "big center" gives him compensation.
Believe it or not, through 7...Qf6, I was following a game between two strong grandmasters! In Marshall-Torre, 1925, the U.S. champion resigned after 7...Qf6. This was an offhand game that they played on board the S.S. Antonia while en route to the Baden-Baden 1925 tournament. Maybe Marshall was seasick. Kayser was not the first player who has fallen into this trap in an Internet blitz game against me. In a 2011 game I played on FICS, rather than play the abject 7.Bc1, White gave up his queen with 7.Bxe5 Bxd2+ 8.Qxd2 Nxd2 9.Kxd2 d6 10.Bb2 (10.Bxg7? Qg5+) exd5 11.cxd5 Qg5+ 12.e3 Qxd5+ and I won.