Could I use a mod that turns all mobs into anime girls its pure visual.

If it's doesn't give you an advantage on other speedrunner than ok you can use it

If its a mod, or a datapack, then no, you can't

thats probably not allowed, cause it would change the size of mobs

@Lang the hit box will not change (if it have behavior pack, you can't but ressource pack yes)

but it would appear as a different size, making some mobs easier to see