So I broke a RSL sin, which was that I used rare characters that I didn't have duplicates of as food for other champs. 

I was googling any info about the fusion when I came upon this video:

https://www.youtube.com/watch?v=k0Q1Va4P5Us

If this video is accurate, I definitely used about 4-6 of the listed rare champs as food very recently (others I luckily still have). My saving grace is that I know there will be events where you can earn the rare champs that you need, but kind of stinks that I wasn't more patient. 

Luckily, I already have basher and at least one of the void rare champs (those I never use as food). 

Hopefully this helps other people (assuming it's accurate).