A mortal brain cannot defeat the elder brain as ithat entity can process all possible moves at once. It is always ahead of you. As the emperor explains, only an illithid brain has a chance to match the speed of thinking to make a move before the brain has a countermove ready.
Furthermore the one who combats the brain also needs to control the protection of Orpheus. So therefore the combination illithid power + orpheus power combined in one, is a prime requisite to move against the brain. So we canhave either Orpheus becoming illithid or an illithid acquiring Orpheus protection power.
I don't know how this works with Tav taking the illithid role though as I never tried that (and don't want to) and a less likable NPC, like Gale for instance, is not allowed to change. So if Tav can turn without eating Orpheus' brain then the story breaks down.
That doesn't make sense, Elder Brains are killed all the time by mortals, without the need of an ilithid traitor.
Neither do have elder brains some special hyperintelligence. They are very intelligent, but so are dragons or even some mortals and no one would buy "to defeat a dragon you need a dragon".
Also "you can't outsmart a bullet", or in the case of D&D a sword. When you are hacked apart with magic weapons as you are big and immobile it doesn't matter if you can think a bit faster than your attacker. You are not playing high stakes chess.
Ok, let me clarify my point. Just to avoid miosunderstandings though, I'm not trying to start a right/wrong discussion. We're nor doing historical research here, but looking at a phantasy story in different ways.
Phantasy needs some degree of suspension of disbelief, opbviously. Why could the one ring not be wielded by Gandalf, Elrond or Galadriël to defeat Sauron easily ? Because Tolkien told you so. Does it make sense ? Only if you (the reader) want it to.
As for the brain's vulnerability. Yes you can harm it with weapons, but first you have to get there. Did you see the scene in Z'rells chamber where she kills her ogre servant just with a thought ? What if the brain can read all your thoughts as they form in your head, and can even predict what they will be before fully formed. You think I have this runepowder bomb that I could lob at the beast, but before that thought is complete, the brain knows you have a bomb on you and makes it explode in your pocket.
Realmspace history is not a good guidcance also. The original mindflayer empire was defeated with the help opf Tiamat. But this brain has evolved with the netherese magic from the crown it now owns. So, it has even more powers than the former empire, coming from old Netheril.
I did wonder about Tav changing though. Although it is a non-option for me in this game, but as confirmed above by Tarlonniel, this breaks the story down if you use it. It would have been better to leave it out altogether IMO.
I don't really like this ending either. I would have preferred a true happy ending. But for a writer it is probably more challenging and satisfactory to come up with something bittersweet or unexpected than a happy mellow end. The difference the writer fails to make, (as I see it) is that this is not a novel or a movie of a couple of hours, but a game where you invest hundreds of hours and really get into the skin of the player character. So the ending obviously impacts me harder. I hope that somehow that message would get through to Larian for their next game.
