Coffee for Dessert

Trade off the guard

16.Bxg4 Nfxg4

White has exactly one piece guarding h2. Black trades it off.

16.Bxg4 Nfxg4
Trade into g4. 16.Bxg4 Nfxg4. A black knight lands on g4, eyeing h2.
17.Nf3 guards h2
The defender comes. 17.Nf3, covering h2.
17...Nxf3+ 18.Qxf3
Remove it. 17…Nxf3+ 18.Qxf3. The guard is gone and the queen recaptured away from h2.
18...Qh2#
Mate. 18…Qh2#. Queen c7 to h2, backed by the g4 knight.

Lesson: Count the defenders of the square next to your king, then ask which one can be traded off.

https://www.chess.com/game/140999279766