These are the 10 enemies he can summon:
If you encounter a rare creature in the wild, you can bring back a small sample of it to Luvannon and he will pay you a small reward and will be able to summon it for you at any time.
He holds the Summoner's Challenge if you have found all rare creatures. It is an event where you battle seven enemies in a row, without items. If you can survive this onslaught you win the Twin Serpent Blade and unlock the Juggernaught medal.