This exists for both the Base Game, DLC, and Both already :)

Base game Low%: https://www.speedrun.com/cuphead?h=Version_1.1-Low-Regular&x=9d8lxv62-ylp6g4rn.0q5wmp7q-0nwpgqr8.013kjprq

DLC Low%: https://www.speedrun.com/cuphead?h=DLC-Solo-Low&x=7kjl0wz2-wl3ddqo8.8104dd5l-wl3d6vw8.21gmr461

DLC + Base Game Low%: https://www.speedrun.com/cuphead?h=DLC__Base_Game-Solo-Low&x=xk95z7g2-wlekk5el.jq6dee71-wlek63rl.xqkvpjkl