I'm pretty curious to how you started a speedrun with Erina and Ribbon in their other outfits without any interaction with the wardrobe. I did try googling for the answer, but to no avail so I was wondering if you could clarify the how
During a Chapter Transition screen, you can hold Magic Left + Magic Right (A + S on keyboard) then press a directional key to switch to a costume. sekrit speedrunner tech
Very late partial answer for you, but they are fighting Irisu while standing on the heal pad at the entrance to the room (which is only possible because they glitched into the room). The Survival badge prevents Erina from being KOed as long as she has at least 2 HP, and the heal pad heals you every frame. Even though the Mortality debuff also means Erina can take damage every frame, the heal pad is still enough that she never takes damage on 1 HP. (At least, this is my best guess as to what is going on.) I think the cake is used to provide a brief healing effect to not immediately die (they drop down to 2 HP for one frame before managing to walk over to the heal pad.) I don't know why Irisu takes damage, though; it looks similar to the Curse debuff from purple boost, except she's not actually cursed; I don't know of any other way for Erina to reflect damage normally.
@@celestialspark5697sounds pretty crazy ngl, I still don't quite get the boss damage part, but to glitch the healing thing to boss room is insane tactic ever, I didn't even notice before, thanks for a very late follow up tho still xd
From what I can see, it's from unequipping the hammer in the menu before entering a boss room. Since then you don't have it equipped, then the free damage begins to trickle. At least that's what I can gather.
So, I'm super late on this, and you may have found your answer elsewhere. Because you can fight Ribbon and Cocoa 1 without hammer using intended methods (necessary for 0%), their HP bars automatically drain if you don't have hammer. This is not true for other bosses, since you are forced to have Ribbon for them (or Amulet in the case of Miru), who would give you the ability to do damage in 0%.