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.