This game was a lot of fun to play! I like the mix between the mandatory captures of checker and the variety of movements of chess. I thought the AI would just make random moves, but it actually proved to be quite a challenge!
The theme of the jam was followed quite nicely. I think the way you framed it (having to lose all your demons before ascending to heaven) was the perfect way to tie it in. This meant the gameplay made sense, instead of just being generic "die to win" instructions.
The music is a good choice and is played at an appropriate volume relative to the sound effects. I love that each type of demon has a unique sound when you click on them.
I like the visual design of the pieces and the board, with one exception. The texture used for the bottom half (rocks?) looks strange when repeated on every square.
Overall, you did a great job! I enjoyed playing your game :)