There's two items counteracting mummification, get both and the boss should be easy.

Also, don't equip cursed items dummy.

Boss is in no shape or form "easy" at this point Id say most people are equipping the cursed item, having no way to remove it is a horrible way to implement a punish/difficulty,  I actually stopped playing after trying to attempt the boss for the 7th time, I just don't have the patience navigating that cluster F#$% of a maze dungeon.  I actually came here thinking the collar was from a previous dungeon or was glitched, and unfortunately this seems like its part of the "trap" of this dungeon.