Hmm... For me it would be:
- No Emperor. Dream Visitor is literally just another adventurer who's trapped in the Prism. The ending can have a moral quandry in regards to either your character (Or companion) or the Dream Visitor being sacrificed using the Prism as the weapon.
- Daisy exists. Separate from the Dream Visitor. It entices you towards using the tadpoles and powers and can grant additional powers beyond that of the tadpoles alone. This can lead to a more involved "Evil" path.
- Tadpole usage being dangerous. Not just eating them, but also using their powers (Both the combat ones and dialogue ones). Having your characters personality shift as their brain gets literally eaten away. With full on ceremorphosis being possible prior to the end, necessitating things like Disguise Self to not be attacked on sight outside of the Absolute controlled places.
- No Mary Sue Orpheus. He can still exist and still be imprisoned somewhere. But none of this "Magical anti-Mindflayer BS". He can have his own storyline in regards to taking on Vlaakith and the future of the Gith.
- Halsin stays in the Grove. Kagha joins the party (If she's alive) as a companion to atone for her mistake.
- BG2 characters like Jahera, Minsc, Viconia are not present.
- More companions available. Such as Mizora (Wyll leaves as a result), Isobel (Sharran Shadowheart leaves as a result), Marcus (Evil path only), Yugir, Lump, Helia, Gandrel (Astarion leaves as a result), a Myconid (Different depending on who you choose to help) etc.
- Additional acts. Have dealing with Gortash and Orin use a separate act each, much like how Ketheric got Act 2. With a final act being the ultimate showdown with the Elder Brain with all your allies.
- BOOOAL provides more content. Clerics that choose to worship him get Blood Domain. Other classes just get an upgradable boon from spilling blood. The Koa-tua show up again in future acts, worshipping BOOOAL or you and having content that reflects this and your choices when (If) you made them initially (Such as giving you gifts of better BOOOAL weapons, their own style of weapons, or they just fight you with increasingly powerful avatars of BOOOAL)
- Actual passage of time exists. Events unfold at specific times. Things like Short and Long Rests advance time. Making them not so free to spam constantly.
- Artificer class.
