If a creature possessed by an intellect devourer is true polymorphed into a creature with multiple heads (i.e. a hydra), what happens?
Is the intellect devourer ejected since at least one head's brain is restored? Does the intellect devourer effectively control both/all heads? Or only one?
Other relevant answers which I'm not re-asking here:
What happens when a creature possessed by an intellect devourer is true polymorphed?