Tactics
Promotion
The pawn reaches the eighth rank and becomes whatever you choose. The tactic is rarely the promotion itself, it is the sequence that clears the way: a deflection, a check, a piece given up so the pawn arrives with tempo or with check.
How to spot it
Count the moves. If your pawn needs two and their stopper needs three to get back, the race is already won and you should be calculating the race rather than improving your position. Watch for the promotion square being defended: that is what the sacrifice is for.
The positions
Easiest first. Every one is from a real game, and the rating under each board is what it costs the players who have tried it on lichess.
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1. White to play Play it out →Answer
29.Nf6+ Bxf6 30.Re8+ Rxe8 31.dxe8=Q#
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2. White to play Play it out →Answer
37.h7 Ne7 38.h8=Q
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3. White to play Play it out →Answer
30.a8=Q+ Rxa8 31.Qxa8#
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4. White to play Play it out →Answer
61.h8=Q+ Kxh8 62.Kf7 a1=Q 63.g7+ Kh7 64.g8=Q+ Kh6 65.Qg6#
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5. White to play Play it out →Answer
26.Qg8+ Ke7 27.f8=Q+ Rxf8 28.Qxf8#
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6. Black to play Play it out →Answer
33...g1=N+ 34.Rxg1 Nxg1+ 35.Kg3 Bh4#
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7. Black to play Play it out →Answer
45...d4 46.f5 d3 47.f6 d2 48.f7 d1=Q 49.f8=Q Qd5+ 50.Kf6 Qf3+ 51.Ke7 Qxf8+
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8. Black to play Play it out →Answer
38...c1=N+ 39.Ka1 Ra2#
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9. Black to play Play it out →Answer
29...Qxd8 30.Rxc5 Re1+ 31.Bf1 Rxf1+ 32.Kg2 Qd2+ 33.Qxd2 cxd2 34.Rc8+ Kg7 35.Kxf1 d1=Q+
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10. White to play Play it out →Answer
50.Rxd2 Rxd2 51.e7 Kf3 52.e8=Q
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11. White to play Play it out →Answer
49.Kh6 Rd8 50.g5 Re8 51.g6+ Kf6 52.g7 Re3 53.g8=N+ Kf7 54.Nf6 Kxf6 55.h8=Q+
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12. Black to play Play it out →Answer
27...f1=N+ 28.Kh1 Nxg3#
Reading about a pattern is the easy half. Motify finds the positions where you missed one, by running your own lichess and Chess.com games through Stockfish, and puts each of them behind two or three puzzles on the same idea so you meet it having just found it three times. See how Motify works.
Positions from the lichess puzzle database, released under CC0.