If I get to make up a dream ability, it would involve an avatar being summoned with its elemental spirit. The spirit would just circle around the avatar and either cast nukes to heal it, or cast nukes on the enemy. Basically a mini version of the V2 avatar fights.

Another one would be to fast in sequence summon all avatars and have them attack with their weakest BP:Rage. It would be fun watching them pop and depop and deliver a small punch to the enemy over and over. This would of course not work solo but would require you to not be hit while summoning over and over (though summoning time would be shorter to make it cooler)