I suppose I'm the only one who would like to see BG3 be influenced also a little bit by Planescape Torment and Hordes of the Underdark.
Other than that, a varied bestiary, my current favourites are: - Beholders and their variations (Elder Orb, death tyrant) - Demilich - Golems: Mithril, demonflesh, - Ulitharid, Alhoon
Quite rare wish: open to expansion packs for when Epic Level rules are released for 5E.
