Slitherbrute can steal buffs, and so is good for Magic Keep at higher levels where the shield becomes impenetrable unless it is stolen.

My biggest fear about consuming rares is that one of them might need to be used for fusion in the future. Even the farmable ones. For instance, I must have farmed 12-6 approx 500 times now, and I've only ever pulled a rare farmable character once or twice. Consuming them, only to require them in the future for fusion, might cost 100s/1000s of energy.

Slitherbrute can steal buffs, and so is good for Magic Keep at higher levels where the shield becomes impenetrable unless it is stolen.

My biggest fear about consuming rares is that one of them might need to be used for fusion in the future. Even the farmable ones. For instance, I must have farmed 12-6 approx 500 times now, and I've only ever pulled a rare farmable character once or twice. Consuming them, only to require them in the future for fusion, might cost 100s/1000s of energy.

Hey op, I ran into the same problem recently and I had to make a decision. do i keep 5 dups of arcanist, slitherbrute, etc

I looked at it this way, I'm in it for the long run, I'll pull them anyway. I just kept the notably better ones.
plus its ok to use up all the farmable rares.

for now focus on your mains
if youre unsure ask away : )

I use the dupes as skill ups and keep at least one copy of each champion. For void/epic/legendary champions I'm keeping at least 3 copies of each since they're way more rare.

I have burned through about 1000 energy farming campaign, and have over 200 mystery shards now. I bet I can pull about 10 rares from these, plus there’s the 4-5 rares I got as level rewards in hard mode. 

 Check their skills and reviews. Bottom line is there are a handful of rares that you definitely don’t need to worry about holding onto.  Let them be fodder for your 4-star champs.