Hey! J.R. here. Dr. Mercury asked me to answer this question because she didn’t know who The Doctor from Gallifrey was. She is totally out of touch with Pop-culture. She spends all of her free time with Chemicals or star-bathing or kidnapping. She once had a TV, but she filled it with fish. I have no idea what that was about – some kind of art instillation? Her feelings on television in the modern era? Just needed a place for the fish? Alas. Who am I to judge?
Anyway, since I AM familiar with Dr. Who and Dr. Mercury, I can answer this question. Dr. Who might battle Dr. Mercury, but since he isn’t a very, well, fight to the death type, and is more of a “run!” type, the way he would battle her would be to try to convince her to become good.
Because Dr. Mercury is a Starchild, an infant among Star-children, growing to her full Starchild potential within the safe womb of Earth. (Because, for a creature that is destined to become a massive energy-creature that feeds on the light of Stars, Earth really is a womb.)
Starchildren can become benevolent forces for good in the universe – or they can become supercharged forces of evil. I think that Dr. Who would do his best to make Doctor Mercury evolve into a force for good, into a creature of compassion, to evolve out of her natal stage on Earth to be a creature whose force of love passes all human understanding.
I like to think that the Doctor from Gallifrey would succeed in this, that because of his experience and his own sense of compassion, he would be able to convince her that creation is better than destruction, that peace and enlightenment have more to gift than all other pursuits.
Of course, as she reads this over my shoulder, she is cackling maniacally, so I could be wrong.