The "notes on the game design" page tells how it works. https://mvasilkov.animuchan.net/king-thirteen

It's just like the game 2048, except with chess pieces. There's a 'play' link at the top of the page.

It's not just like 2048 though, since you only move one piece at a time. In 2048 you move all the pieces in the same direction at the same time.

Indeed, that was the first thing I tried (using arrow keys) and when nothing happened I said, "Oh so it's not like 2048 at all, okay... let me check the game instructions since I'm lost now."

and then there's no instructions :clownemoji

agree! how to play??? I found I can click and join knights by knight move with the same subscripts. but what is the king doing? there are no directions and its not obvious!

The king has just taken my largest piece after no moves were left. I guess when you reach 2048, you can take the king and win.

Apparently he is worth 1024 so you can take him when you have a 1024 piece, and win. I didn't realise this (or that he takes pieces when cornered - I avoided that, assuming a stalemate would mean losing) so played it right through to a regular 2048 which took a verrry long while.

Open game. Random clicky. Ah!

Yeah I am very confused. This isn't like 2048 at all. The pieces move individually? And why are there multiple different colors of knights? What is the king doing? How do I mute the game entirely?

Interesting take but needs some more polish and a good demo video or something.