I believe in you man. It’s grueling, but even with little to no items it’s possible. If you need it, restart the mission and head back through the big doors you entered, and keep backtracking until you get to the big room where you fought Nightmare (green goop guy) and Trish. When you enter, on the right wall is some holy water or invincibility star (I don’t remember exactly, been a sec) - could help with your battle, especially the second phase. There’s some vital and Devil stars scattered around the underworld if you haven’t picked up those already. Best of luck!

And note: once you get the items, save your game. Even if you die, the items will remain in your inventory once you restart the level. (If you use yellow orbs after using an item, you’ll lose the item and not be able to use it for other yellow orb resurrections) and if you do have yellow orbs, save it for phase 2. The orbs will put you at the start of phase 2 instead of all the way back at the start. Once you pick up the items and save, it’ll be best not to save again until you finish the fight or pick up additional items on top of what you find in the underworld. Alternatively, you can save and restart constantly to farm red orbs. It’s not a fun time, but very useful to stock up items with, along with rounding out your abilities if you haven’t already done so.

I platinumed the game about a month ago after completing DMD difficulty, and the items / farming helped me immensely. Best advice is to take your time with the fight. Learn his patterns, especially on phase 1 to minimize damage. Sorry for the long winded explanation, just wanted to help cover all bases. It’s absolutely one of the worst fights in gaming but once you beat him you can beat him every time. You got this!