"The ending changes depending on how you used the tadpole"
I hope not that would be derivative garbage. There are hints of the magic used that corrupted the tadpole. The magic is from an ancient very magically powerful race of humans that exist in pureblood form in small communities. I am unaware of any other race familiar with said magic so it could be this race of humans manipulating the illithids to destroy the cultures that destroyed them. Hence the "not transforming" but the ability to use the very powerful abilities of the mindflayers. The tadpoles maybe a symbiote weapon able to easily infiltrate all levels of current society to destroy it from within. Using a corrupted elder brain to direct the infected. This elder brain would be the "absolute".
