Good game . . I would also advise to make the pixel size same of all characters (the player and larger enemies, boss look very different). I made the same mistake.
Viewing post in Run and Gungeon jam comments
Unfortunately the artwork was kind of slapped together as we lacked a dedicated artist and had to borrow a menagerie of random open source top down assets instead. The enemies were all from the same pack and had the same dimensions in pixels so we just had to work with that so we could focus on the coding.