I have more questions than theories, really.
We know that the crown originally was intended to attract and absorb magical knowledge, while granting them dominion over themselves and keeping them apart from the Weave. One of Gortash's notes states that they reversed the dominion effect so that they can influence the crown's wearer instead. Because they apparently didn't do anything about the other functions of the Crown, the Elderbrain evolved.
But what does that mean for the tadpoles. From what we learn from Wyll, his tadpole messes with his magic. The tadpole also seems to mess with Gale's orb, and protects Astarion from both Cazador and the Sun. I think none of the girls ever comment on the tadpole messing with their abilities in any way that an ordinary tadpole wouldn't. Karlach's heart-issue is explained by Faerûn being colder than Avernus.
We are also told that each time we use Illithid Wisdom to bend someone to our will, that we loose something of ourselves, though it isn't clearly stated what exactly we are loosing - a memory, a bit of our soul, a part of our personality?
Astarion being severed from Cazador makes sense, as the tadpoles are tools of domination and the tadpolees should only listen too one master. But what about the tadpole's magic protects Astarion from sunlight? (Though that might be a remnant from Karsus's Weave and the Shadow Weave having at one point been one thing.)
Magical absorbtion and separation from the Weave would explain both Wyll and Gale's problems. Having two magical absorption devices inside of you can't be good. Which makes me wonder if, once Gale's orb was stabilised, was the tadpole also connected to the Weave through the Orb? Also if the tadpole hinders Cazador's influence over Astarion, why does it not influence Mizora's power over Wyll? Or is this the reason why his warlock powers have weakened?
