6. Skeletor (He-Man And The Masters Of The Universe)
As powerful as Skeletor is, and as wonderful as the interactions between him and the Doctor would be, Skeletor just isn't bright enough to pose any real threat to him. Don't get me wrong, Skeletor has done things that suggest an intellect way beyond anyone in the real world - some of his inventions have been fantastic and to have learned magical abilities of the level he displays means he's certainly not unintelligent - but that doesn't mean he's not a complete idiot with the common sense of a potato. Skeletor's complacency, arrogance, naivety and aforementioned lack of common sense is his downfall. The Doctor would take the proverbial p*ss out of him in a battle of wits. And let's not forget that the Doctor's technology is every bit as good as, if not better than, anything Skeletor has ever created. Skeletor only ever poses a threat to the muscle-bound Eternian He-Man because it's mind over muscle. But in a mind versus mind battle with the Doctor, there would only ever be one winner. P.S. It's
not Skeletor.