This is probably a really dumb idea, but what if during his E, Garen grounded himself?
He can still move about and whatnot, but while in his E animation he's not effected by pulls, knockbacks or knockups (basically any displacement CC)
Meanwhile at the same time he can't flash or use any sort of means to dash (ex. protobelt)
What would happen?
######This was a sleep depraved idea I had at like 5am yesterday, so yeah, it's not gonna be the most thought out thing ever