The idea is really interesting, I enjoyed creating monsters and fighting. Also the art is cool, you certainly found a very interesting style.
I've encountered a crash, I guess, when you create a monster and place it to the slot, you can somehow end with an empty frame around cursor, and then if you click on the monster creation slot the crash happens. But it's a strange case and it's easy to avoid.
Overall, its a cool game, really fun to play. Nice work!