Mate in 9

The bishop on f1 pins the rook on g2, while the knight on h6 keeps watch over g4. If either moves, Black will begin to unravel their kingside forces. White must therefore summon the rook from a1 to stir up mating threats, for the knight on c8 lies too far afield to enter the fray.

1.0-0-0! (threat: 2.Rd3#)

The quiet try 1.Rd1?, also aiming for 2.Rd3#, is parried by 1...e4!, leaving White without a continuation. So instead, we turn to the more flamboyant 1.0-0-0. And yes, castling is legal — this is chess composition, not tax law!

1…e4 2.Re1 (threat: 3.Re3#) Bc7!?

If 2...Bb6, then 3.Nxb6, and 4.Re3# is unstoppable.

3.Re3+ Bg3 4.Nb6!

White parts with the c8-knight to avoid stalemate, and in doing so clears the path for the a6-pawn’s promotion.

4…axb6 5.a7 b5 6.a8=B!

A necessary underpromotion — the humble bishop in place of the haughty queen — to offer Black just a sliver of breathing room and avert stalemate.

6…b4 7.f4! exf3 ep. 8.Bxf3! B-any 9.B3xg2# Neat!

The solution weaves in all three special moves of chess — castling, promotion, and en passant — thus completing the well-known Valladão task, that elusive trifecta beloved by composers.