Best I've seen so far is earned from class world random event, called Magichange Guild: Increase stats by 30% x the # of allies equipped with Magichanges Imagine 5 characters with magichanges, each getting +150% stats from this evility alone!
Probably not even the best evility out there, but I'm enjoying it.
Another nice evility I found in class world is Saintly Aggression: Increase Normal ATK by 100%. Works great on Heart Cannon Club!
Proud Hikikomori. It's not a mental disorder, it's a lifestyle choice.