Avi is a cosmic entity from The Basement. While creatures from there were meant to stay in the shadows and control things beyond the scenes, they had different motives.
They murdered numerous of their own people and escaped. They resurfaced trillions of years later, started an empire, became a colleague of Delimangur and started attacking and taking every Verse in sight by exploding them from the inside.
They fought Bongus and were heavily injured, but escaped to a personal verse they created, The Attic. They healed their wounds and are still continuing their crusade across Reality.