Parasite could also be cool for a sequel

That's how Parasite often gets used, after any initial outing that gets to set the stage and have Superman fight off some problem just to let the world know how powerful he is.

At that point you have various groups trying to replicate him, imprison him, blackmail him, fight him, or steal his powers.

The above list more or less means villains such as Cyborg Superman, The Preserver, Lex, Mongul, and Parasite respectively.