After seeing enough compositions by Blathy, it's clear what the first 20 or so moves will be. The end I had to think about a wee bit. Too bad about the dual on the very last move. (24.Bc6#)
The Problemist problem. Mate in 24 moves

The last move can be either by moving 24.Bc6# which was the main square for the bishop to find and the other is the pawn 24.b3#. If black does everything right he can prolong the checkmate to a maximum of 24 moves but it's pretty hopeless for black either way.

I'm pretty sure the last moves must be 22... Nd2+ 23. Bxd2 23... e1=Q 24. Bc6#. No dual.

Black isn't forced to play 22...Nd2+, but that must be the move in the puzzle to have only one correct continuation.

Black isn't forced to play 22...Nd2+, but that must be the move in the puzzle to have only one correct continuation.

This is not a problem that I made. It was made from a person in a newspaper called The Problemist. I found it in a youtube video that was explaining this problem. Here is the link to the video if you want to see more about it: https://www.youtube.com/watch?v=1BuLsK2o6XM
This is The Problemist chess problem. Hope you will enjoy it! :)
Hints for White: Only one piece can move, if you move any other you will let the king escape or check your own king.
Hints for Black: No piece can move except for the pawns, else the checkmate will be shortened.