This one gave me some fits, until I got to the question, "what's the absolute minimum material I need for a mating net here?"
Black has 4 checking moves, and White only has 3, and again the only clean check, 1 Nc7+, is cleanly answered by Kb8 with no good followup.
The pawn on b7 is a big nuisance, able to either b6+ or bxa6, removing a key mate-net piece. So how about Bd5, pinning it? Nope, without a check, Black can give her own check Bb6+.
So we're down to sac checks, but neither sacking the rook nor the queen allows the other one to mate, and surely they can't both be sacked, right? Unless that is the whole idea, and yep, it is.
1 Rc8+ Nxc8 This both keeps c8 blocked to the king (later) and removes control from d5 for the bishop.
2 Qxb7+! Removing the pest directly.
2...Kxb7 3 Bd5#
As with #4014, the king has been trapped in a corridor, this time a diagonal one (a8-h1), with a closed door (c8), and executed there.