Glad you enjoyed the game! I did end up altering the three-slugs room during development to allow you to defeat them with falling arrows (arrows will dislodge and fall when you fire at a wall up close, and I ended up liking it as tech to defeat certain enemies), but I do think the lava-themed rooms with bats ended up being a little harder than they needed to be. I have gotten a similar comment about how shooting the bats in the room with three of them only makes the room harder to complete than it initially is, haha.
Does your controller come with software to map buttons to keyboard inputs? I know others who wanted to play some of my games with a controller as well, and that ended up working for their needs. I have been interested in implementing custom keybinds for future games if it feels warranted, but it's something you have to specially program for in GMS. I would have to rewrite and reorganize a bunch of this game's code for it, and yeah, it's just something I wanted to quickly throw together.