This game has a really fun lighthearted feel. The voice changer lines are barely audible but just having that gives it a fun atmosphere.
I think my main issue is how it feels to play the game (partly being the keybindings just being unusual to me). It is barely possible to do any auto shooting while casting other things and there's little reason to switch up when you found something that worked, all spells just kind of have the same reason to exist none really feel like they have a special reason. Maybe they could each have more special effects or just be a bit more spammable so it can give the power fantasy of a boss with many moves.
But I think with a bit of balancing I could have a lot of fun with this, it just doesn't feel like you're being particularly powerfull when you play the game.
Another thing, I think you have some setting wrong on the textures, their blurr looks a tiny bit like what you get from Biliniear filtering. It interpolates between the pixels instead of just cutting off as is usual for pixel art (there nearest filter is usually used). But I haven't used GameMaker so I can't give any specific advice.