Hero coach takes any legendary hero (legendary only) and maxes them out. “Hero will be leveled dup to level 90, ascension level 4, and twice limit broken. The gem cost of training a hero is reduced if the hero has been leveled up.”
“Train one hero per event”
“heroes that were released 731 days before the start of this event”
Gem cost by hero level (I only have certain options to test here):
1/1: 1000
1/6: 981
3/45: 428
3/49: 413
3/70: 334
4/80: 37
4/85: 18
I don’t plan on using this for heroes at 1/1. But heroes at 3/70, I’ll do it. Even better for a hero at 4/80.
FYI this does not level up costumes.