With the first "Doctor Strange" movie is such a huge success. It is the 14th movie within the Marvel Cinematic universe and not only that, it has already crossed 300 Million USD in terms of box office money. 

According to Screen Rant, a sequel is pretty much guaranteed. The reason for that is also the final two scenes that appeared at the end of the first movie. The first scene with Thor and the second scene with Mordo. 

There have been many wants and expectations regarding what should happen in the second movie, and it is safe to say that people have been putting up their own projections and ideas as well. 

Movie Pilot  referred an entire list of five villains which will be a great catch for the second "Doctor Strange" movie. A lot of these are very good choices and will work wondrously with the upcoming second film.

The first and most obvious choice is Baron Mordo. At the end of the movie it is seen that he turns evil due to his master, the Ancient One betraying him in his eyes. He was Strange's biggest friend at first but according to comics he will be his biggest foe in the future.

Second on the list is Nightmare. Nightmare comes from the Dream Dimension in the comic books. Since there are unlimited dimensions he basically controls the dimension in his own dark ways and uses various psychological warfare against Strange. 

Then comes Umar who is a female that comes from a specie of energy beings. She is highly intelligent and powerful. Being Domammu's sibling, she could most likely appear in the next film to take revenge on what Strange did to her brother. 

Afterwards, there is Mephisto who is a highly demonic and powerful character created during the Silver age. He is all evil and nothing but evil. He is immortal and was even once known to feed on human evil.  He even stalemated Galactus, which is one of the most powerful characters in the Marvel universe. 

Morgan Le Fay is the final villain. She is also immortal and she used that time to indulge herself into mystic arts. She is considered one of the most powerful sorcerer on earth and so she could prove to be quite the match for Strange. 

These are the five villains anyone would love to see in the next movie. Considering how they have been battling Strange in the comic books for years.