11

As you deliver checkmate with the rook on the 5th move, Swindler claps his hands. "Not bad! The elves of the North Pole have been scratching their heads over this one for ages. Thanks for helping me clinch the first prize in the prestigious Annual North Pole Rook-on-a1 Solving Championship," he grins.

Frustrated but hopeful, you ask Swindler about the mysterious letters. "Who's writing them?" you ask. "I have no idea, I just needed the answer to that puzzle," Swindler grins.

As you step forward, ready to strangle him, he jumps into his car. "Just part of the game!" he calls out, starting the engine.

As his car swerves down the snowy road with the trunk still wide-open, a shower of styrofoam flies everywhere.

You're stumped, but not ready to give up. The bell from the old North Pole church rings, and with no other plans in mind, you decide to follow its call, hoping it might lead to some answers.

Inside the church, you find a small, leather-bound book titled "Secrets of North Pole Chess" at the altar. Within its pages, there's a note about "Alexander Grinchuk," an elf who took a dark path. The legend describes how Grinchuk tried to steal Christmas over a century ago, prevented by the other elves. No one had seen Grinchuk since that fateful day, but now you start to wonder if he could have returned, and if he is connected to the mysterious letters and the disappearance of Maskenissen.

Along with this information, the note contains a new puzzle. It seems to be connected to Grinchuk in some way.

This is another selfmate, where White, moving first, must force an unwilling Black to deliver checkmate (Black will always pick another move than mate if possible). Give the sequence of moves that forces Black to mate White on the fourth move (both White and Black alternates, making 4 moves each). Here's the position on Lichess, and here's Offerspill Discord's server, if anything is unclear.