The tadpole doesn’t kill you or take over your brain though
You know, that might have been cool, though.
Imagine if the tadpole's hold on you increased over time. Every so many long rests, the character develops another tadpole power. You don't choose them by getting extra tadpoles, but rather the power simply develops.
And just when you get all the powers... ceremorphosis. That's it. You cease to exist and a mind flayer is born.
