Just an idea for a quest and reward item for to make a summoner's life even more difficult and miserable.
After having completed Mama Mia, return to Mamaulabion to activate this quest.
Obtain the following seven items from the seven High-tier Avatar Battlefields (Items would Rare/Ex and a treasure pool item) after defeating the corresponding avatars in the battles listed below, plus your Evoker's Ring:
★Trial by Fire (Ifrit): Egil's Blazing Torch
★Trial by Ice (Shiva): Improved Rust 'B' Gone
★Trial by Wind (Garuda): Sparkling Bubbly Water
★Trial by Earth (Titan): Dry Desert Light
★Trial by Lightning (Ramuh): Elder Timeworn Branch
★Trial by Water (Leviathan): Third Eye of Nept
★The Moonlit Path (Fenrir): Ancients' Antique Key
Mama Mia : Evoker's Ring
Return all eight items to Mamaulabion (The items must be traded one at a time and it is not necessary to turn in all seven at once).
Wait until midnight (JST), then speak with Mamaulabion once more to receive the Convoker's Ring.
Note that the quest is only repeatable if Convoker's Ring is dropped.
That, or just a rare drop from a future battlefield ★The Moonlit Path (Fenrir) or ★Waking the Beast (Carbuncle)