How will White give a checkmate in 2 moves? Which tactical themes are used?
White could give a checkmate in 3 moves in many different ways; for example, 1.Qg6 h6! (instead of 1...hxg6 2.Rh1X) or 1.Qe8 h6 "save" Black for one extra move. However, there is only one way to give a checkmate in 2 moves.
This blockade prevents Black from moving the h7 pawn, which would create an escape route for the king.
Black is in zugzwang, that is, put at a disadvantage because he has to move. If Black could skip his move, White wouldn't have a mate in 1 move!
Other moves don't help either: 1...g6 2.Qxf8X because White's queen had pinned the g7 pawn. Moreover, all the bishop moves are followed by 2.Qxg7X.
White's rook, too, had pinned the g7 pawn, which was the main idea of White's first move, spectacular queen sacrifice.
(The combination was published in the Finnish SHAKKI! magazine in January 2011.)