Avalon is a legendary island, originated from the Arthurian lore, as well as in other adapted medieval folklore myths. A magical place, often self-proclaimed as the Isle of Fruit Trees, Avalon is famously known as the resting place of Arthur Pendragon, after his final battle, as well as the origin of the Excalibur's sword. In other myths, Avalon seems to be inhabitated and populated by magical beings, including fairies, where they appear as subjects to the fairy king, Oberon, as well as to his consort, Titania.
Regarding the villain tournaments, the Gargoyles version of the fantasy realm appears in the second and third Disney vs. Non-Disney Villains War, as well as the second Disney vs. Anime Villains War, as the home of Oberon, and of his children. It is also featured in the second Disney vs. Marvel Villains War, though serving as one of the base of operations of the villains.