I feel that there are two possible answers to this question. @Guvnor swerved, but I ducked…
By “the full costume bonus”? Do you mean the total 5%, 5%, 10%, 5% thing? Yes? Then, no! Until the special skill is maxed on the original and the costume and both are fully levelled up, your bonus will not make it past 3%, 3%, 6%, 3%. BUT: you can stop with the original having just completed its final ascension (+ the costume of course) and then just max the costume first (knowing that you will be stuck with the 3, 3, 6, 3 bonus until both are maxed). This way you get a bit over half the benefits of the maxed costume for cheap (until you can level up the rest of it!!)
@Guvnor was correct, @sft1965 was incorrect (or we talked past one another). A maxed hero at 6/8 with costume maxed at 8/8 does in fact get the full 5%/5%/10%/5% bonus. I have Tyrum in this state right now. (Though I will go ahead an max his base hero for flexibility.)
Actually I am certain you are the correct one here! I’ve been wrong about a host of things before now!
I have only leveled up a costume on a special skill maxed haro. In all cases I have never gotten, to my knowledge, the full bonus until the costume was maxed along with the special skill of the original hero or the costume and the special skill maxed with the hero…
EDIT: sweet mother of mercy, I went to look and my 3 costumed heroes waiting for final ascension are not special skill maxed as I had previously thought: 5:8, 6:8 and 7:8.
Sorry to have wasted your time. A million apologies.
I have several costume dupes. They were saving for my heroes for later on in the development because the exp gain is massive. They nerve the exp quite a lot so I’m using them now.
I have Li Xui costume dupes:
v28 Li Xui custome → 36.600 exp
v29 Li Xui costume → 13.800 exp
So based on the table it roughly need 595 feeders to feed a costume 5* from zero to 4.80 right? (Assuming that it is mixed color of any 1* and 2* from tc.11), am i right?