The zwischenzug ( Or if it involves a check we can say zwischen-check) is probably my favorite all time tactic. Why you ask? Well…
…It’s really, really hard to win a chess game. The opponent your playing may know just as much if not more than you do. A zwischenzug by its very definition is not the expected reply. To win chess games we often need to play moves that are not obvious. So I believe psychologically a zwichenzug is a hard move to play and find.

Wikipedia defines a zwischenzug as follows:

“The zwischenzug (German: pronounced [ˈtsvɪʃənˌtsuːk] “intermediate move”) is a chess tactic in which a player, instead of playing the expected move (commonly a recapture), first interposes another move posing an immediate threat that the opponent must answer, and only then plays the expected move (Hooper & Whyld 1992:460) (Golombek 1977:354). Ideally, the zwischenzug changes the situation to the player’s advantage, such as by gaining material or avoiding what would otherwise be a strong continuation for the opponent.
… Such a move is also called an intermezzo (Cox 2007:216), intermediate move (Kasparov 2008:208), or in-between move (Burgess 1997:494) (Horowitz & Reinfeld 1954:180–97). When the intermediate move is a check, it is sometimes called an “in-between check” (Horowitz & Reinfeld 1954:183–85), “zwischenschach” (van Perlo 2006:479), or “zwischen-check” (Mednis 1997:270).”

So at this point if you’re an experienced player you may be thinking yeah zwischenzugs or if it involves a check zwischen-checks are pretty cool and you may play them fairly frequently. This may be true but I bet after a loss you see that geez you didn’t have to play an immediate recapture or response to a threat but had a winning zwischen-check or zwischenzug.
I believe if you always have your mind trained to think of this type of non-obvious tactic you may win more games.

Below is a game I played this weekend in the Dc Chess league with 2 zwichen-checks . My opponent played one that didn’t work which shows there can also be a dark side of this type of move if not careful.

DC Chess league Match on 7/14/2017.  I’m wearing the Baltimore Orioles hat.

White: S.Hoshall 2227 Black P. Collier 2206
DCCL Chess League 7/14/2017
1. d4 Nf6 2. Nc3 c5 3. dxc5 e6 4. e4 Qa5
5. Bd3 Nc6 6. Nf3 Bxc5 7. O-O Qc7 ( white has more development but the position is closed now so Black can play a move like Qc7 that doesn’t develop) 8. Qe2 a6
9. h3 Nd4 10. Nxd4 Bxd4 11. Be3 ( From white’s perspective you generally don’t want to trade with more space but the black bishop is a pretty good piece, more active than white’s bishop so White trades off blacks good bishop. White also offers Black the chance to win a pawn which would give white the initiative if black takes the knight. He refuses) Bxe3 12. Qxe3 d6
13. Rad1 (Rad1 is a positional solution, Pressure on weak d6 pawn and grabbing open rook file but better may be grabbing more space with f4) Bd7 14. Be2 Bc6 15. Nd5 ( Stacking the rooks on the d file with Rd4 is simple, better and more consistent with white’s original plan of Rd1)) Bxd5 16. exd5 e5
17. c4 O-O 18. f4 ( double edged, f4 opens the position and will give both black and white some play) exf4 19. Qxf4 Rae8 20. Bd3 Re5
21. Qh4 Qb6+ 22. Kh1 (white has threats that Black must counter) Rh5 23. Qg3 Qxb2 24. Rb1 Qd4
25. Rxb7 h6 26. Re1 Rg5 27. Qxd6 (Black cannot take the bishop on d3 because of forced mate 27…Qxd3??, 28.Qxf8+!, Kxf8 29. Rb8++white is winning now but must be careful with 3 pieces attacking his exposed king) g6 28. Qb6 Qc3
29. Qe3 Re8 30. Re7 Rxe7 31. Qxe7 Nh5 32. d6? Qd2 (beautiful move, Blacks queen is threatening checkmate among other pieces and white cannot defend easily.)
33. Bf1 ( Best try, if only white had one more move to play 33.d7 but he doesn’t because of 33…Qg2++) Ng3+ 34. Kg1 Nxf1 35. Qe2 Qd4+?? (Black plays a zwishencheck, Going into drawn ending is Qxd6, Zwischen-checks are often good and this provides white another opportunity to make a mistake with Kxf1?? But in this case it is a mistake.) 36. Qf2 Qxd6

White has 3 ways to take the knight in the above diagram. All of them win the piece. But white has a zwischen-check that wins.
37. Re8+ ( A zwischen-check that wins for white, before taking a free piece automatically see if you have a better move) Kg7 38. Qb2+ Qf6 (if f6, Qb7+ leads to mate, danger of exposed 7th rank. Have you ever had a coach tell you to be careful about exposing your 7th/2nd rank with no pawns? This is why. ) 39. Rg8+ Kxg8 40. Qxf6 Ne3
41. Qxa6 (white will get a queen fast while black captures a few kingside pawns) Nxg2 42. a4 Nf4+ 43. Kf1 Rf5 44. a5 Nxh3+
45. Ke1 Ng5 46. Qc8+ Kg7 47. a6 Ra5 48. Qb7 Ne6
49. a7 Nc5 50. Qb8 1-0