The concept of this game is interesting! There is a lot to play with for the future if you plan on further development. You can try having obstacles that obfuscate the view, similar looking characters, stuff like that. Though I do think it's a bit unfair that shadows spawn overlapping each other. And having to wait for a refresh when the character you have doesn't have a shadow on screen also drags the player experience down a bit. Consider maybe adding some features such as a "holding" slot that you can temporarily swap out the character you're holding, like how Tetris does it!