Event Quests give you free shit during events, like during Advents, clearing Ultimate with a R team will give you a Dragon Eye Shard. Once.

Accessory Quests are what will be our hardest content I believe, the highest difficulty basically only being possible for whales with perfect SSR teams. Supposedly. You get accessories (you know, rings, earrings, stuff) as rewards which are... uh, I dunno. Elemental attack for specific teams I guess? I haven't really looked into it. I probably should've, but eh.

I think upgrading these accessories will be extremely Gem intensive, as I think I read that that part is getting nerfed even harder than Awakenings are. To a fraction of the original cost.