You totally called it! The dev is a huge Enter the Gungeon fan, haha!
And about that music—yeah, it's a total bop! Full disclosure, we actually found it as a free track on Pixabay (it's credited in the submission) and the vibe just fit so perfectly we had to roll with it (⊙o⊙)!
This is actually my first time making a bullet hell, so the pattern design definitely still has a ways to go. But maybe luck is part of the game? Every time you charge up, you're gambling on whether the Cookie King will give you the chance. :)
Your thoughts on the difficulty are spot on, too. The original plan was even more punishing: one life and one single shot to kill the boss. After playtesting I was like, "yeah, that's way too brutal," so that became the hard mode. But I'm seriously thinking about nerfing some of the hard mode attack patterns and mixing them into easy mode to give it more variety, just like you suggested.
Thanks so much for your suggestions!