Well, there already exist items in game to get avatars/pet boost to all stats. Unfortunately, avatar being in the nature of being easily resummonable doesn't need to "rage". Nor do they especially need a 2 hr duration. Think a 30sec duration would be more reasonable to get the "bump" whatever it is based off move.

Hey what about a "Souleater" move for avatars, that consumes HP or MP of Summoner?