This is the latest in Schultz's series of chess puzzles, some of which have a series of increasingly difficult simple puzzles, some of which focus on one or two challenging problems.
This focuses on a single endgame position. I struggled with it a bit; not being a chess person myself, some of the rules involved were a bit arcane to me (like the stalemate rules). And perhaps my biggest problem with the game is that the author assumes familiarity with how endgames run, making seemingly useful moves end instantly without much explanation (most were generally well explained, I'm just salty because I don't see how pc7 kc5 where the rook goes to d1 is a stalemate; I wish that particular one was either better explained or if it let the player make the move and try for a turn or two more before shutting it down). So I just had to rely on random guessing for the first few moves.
I thought about searching for help, and I did look on the forums, which reminded me to read the documentation, which helped me grasp things. In the end, it was satisfying. And I think that this was the most emotionally poignant of the chess games; while my main attraction to this game was the puzzle, the emotional aspects were a nice touch and well-integrated.
I do think there is a mistake in the verbs section (correct me if I'm wrong):
It says (Spoiler - click to show)"You can also say N to set (or re-set) the default piece to promote to, say, the knight. In this case, although K is usually the king in algebraic notation, K is referred to as the knight, since you can't have two kings on the board," but typing N just moves the king up a square. To actually change the promotion you have to type the letter of the piece you want to promote to after the move, like c8b for bishop. As written, the text implies that typing N lets you select what you promote into.