4. Jasmine - Angel
Imagine the Doctor having to deal with a villain who appears to everyone around him as a bringer of world peace! Jasmine's power is such that anyone who sees her - whether it be in person or or television - or hears her voice falls under her blissful thrall, while she keeps herself all-powerful by devouring people whilst in her true form - a huge tentacle monster. I envisage the Doctor being able to see right through this, by virtue of his vast intellect and enormous willpower, so it would be very interesting to see how he would convince everyone else about her true intentions - including his companions and those close to him, who would undoubtedly all fall victim to her powers. Jasmine also presents something of a physical threat - possessing strength enough to manhandle the heroic titular vampire
Angel and use a mini-van as a projectile, as well as shrugging off a huge electric shock like it was nothing, both whilst in a supposedly weakened state. The Doctor would have to figure out that, to defeat Jasmine, her name needs to be spoken, and he would thus need to travel to the dimension of the Keeper of the Name, where he would encounter giant insectoid creatures and demonic guards. I think the interactions between Jasmine and the Doctor would be fantastic. And seeing him pretend to be under her thrall as a means of finding out more about her would be funny as hell.