Best Use of "extra" Epic Champ

keep for possible fusion

100% keep for a fusion.

Umif it's a great epic you are using, then yes keep an extra for fusion as you would like to use a toon you need. But if its an epic u don't use, why keep 2.. I use the 2and for food

Use as a book if you haven't booked her A2 skill yet. That's the important one if you're using her as a turn meter boost in either arena or CB. If you want to take advantage of her enemy tune meter down abilities (which works well for Spider and FW), then she'll need to be fully booked.

For a champ that I think I'll actually use I might use the 2nd as a book, for a champ that I know just has no utility or is just sub par I keep one copy for a fusion, and food the rest. If Storage space were free or even cheaper I might keep more (I USED to keep 2 of each epic I came across) but now I have nearly 1 of every rare and 2 of many epics so when a Fusion rolls around I get hopeful that I can use those saved up Epics but nearly every time a fusion comes around only 1 if any of the eipcs already on roster are part of the fusion. Often you need completely new champs and so saving them doesn't help. This isn't always the case mind you, and thanks to saving epics the Cillian fusion was so easy I almost forgot to fuse him. I guess there is no wrong answer, but for me, for now, I'm fooding epics that I already have 1 of and have no use for.

Considering they used her as a fusion epic, I’d definitely save another copy. Plarium pulls that stuff quite frequently.

Foods a waste, use her as a book if ya want but khatun isnt a very good champ. Id just lock her away in the vault. I have like 100 garbage epics in my vault incase of fusions or reworks/buffs