Advent of Chess 2023 - Day 8

The door integrated into the chessboard opens, revealing a staircase spiralling into the depths beneath the North Pole. The underground chamber you enter houses an illuminated chessboard, set mid-game with only six pieces left on it.

In the corner of the chamber, you see something that scares you – a torn Santa mask. This indicates a serious problem: Maskenissen might be in danger.

Beside the chessboard, you find a letter. It reads: "I want to play a game. This is a helpmate problem. With Black to move first, how can White, with Black's assistance, mate on the fourth move? Black plays 4 moves and White 4, and White's 4th move is mate. If you are confused, check out Offerspill's Discord server. Also, here's a link to the position on Lichess. Make your choice."