I assume the tentacle breaking through the ramparts belongs to an Elder Brain, one with as yet unheard of size. Since what could the Absolute be but a massive Elder Brain?
The Absolute could be SO many things.
1. Melyssan reborn because of the Second Sundering, out for revenge and godhood. 2. Bhaal, Bane and Murkyl fooling everyone to reclaim full godhood. 3. A Demon or Devil Lord like Zariel or Baphomet who were key characters in Descent Into Avernus 4. Shar 5. Cyric 6. Irenicus 7. Your character from the first 2 games. 8. Ah heck. Just about anyone.
The point is, the Absolute's identity is wide open right now. It really could be anybody.
