this game is absolutely phenomenal, the core gameplay extends to other interesting combat patterns and enemy interactions super super well. Definitely a stand out game out of all the other games I've played so far. The bat boss fight was frustrating but in the best way possible.
As the other commenter said, I would have liked some aim assist with the grappling as well, since I feel like the game should reward your decision making in terms of what to grapple to instead of rewarding the degree of precision you have in aiming your hand throw, but that's a super minor nitpick.
This isn't a suggestion or even feedback as I'm not sure how it should honestly be, but I'm split on whether or not your character should have some or any invincibility frames during the grapple travel. I found it weirdly frustrating sometimes that some bullets seems undodgeable because they were coming in from the exact direction of the grapple, but it could also end up being overpowered and might require some clunky workarounds in terms of animation timings and cooldowns and stuff. Just something to consider I guess!
I loved every single second playing your game; it was a perfect example of doing a lot with a little, especially in a 10 day time frame. Congrats on the submission and awesome work!
I see that you're using GameMaker, but if I may ask, how did you manage the boss and enemy behaviors and switching in between phases? I'm assuming you used a finite state machine, but every implementation of that I use in Unity seems really clunky and awkward to work with, so I was just wondering what kind of options you have in that game engine.