Outside, he is a planet devouring monstrosity, getting more powerful and more dangerous with each one he eats
Inside, there's his antibodies, who are amalgamations of his victims that try tear apart anyone who manages to get within him.
Among the detritus inside Unicron is a mural of a Quintesson. It inspires fear from Bumblebee, and is an ominous reminder that any Transformers universe is vast and contains many, many threats and eldritch horrors. Even if Unicron is defeated, there could very well be this unknown horror waiting for the Cybertronians…
