5. Brainaic
Brainiac is an AI who collects all the information of a world and destroys said world, thereby making his information more valuable. He travels across the galaxy to world after world and won't stop until all life is extinguished, completing his program. One of the most notable aspects of his character is he attacked Krypton at one point, shrinking the city of Kandor into a bottle and taking it with him. It may be a bit too soon to introduce Kandor since it runs the risk of using a "We can bring Krypton back" plot again; but, Brainiac has been a villain fans have longed to see. He's not only extremely intelligent he's also a physical match for Superman as well as sharing personal history with him. Though it would be great to finally see Brainiac in the sequel, his story and the potential I see is very similar to what Snyder and Goyer did with Zod in Man of Steel, making the likelihood if his appearance so soon very small.