Probably is going to be the Inventor since he was the first true villain Ms Marvel faced in the comics, but he's kinda lame. Stormranger is good, but the first season seems too soon for an evil doppelganger (more on that latter). Thus we have a toss up between my two personal picks: Lockdown and Doc.X. Lockdown is another Carrol Danvers fangirl, but went on a more extremist path than Kamala. The series could present her as a dark mirror of Kamala, something the comic didn't (or maybe failed) to do. Doc.X would be a more risky choice as it is a sentient virus that is an internet troll (quite literally as it usually takes the form of one). It is one of Kamala's more memorable enemies, and as an agender being that can take on various forms, they could use multiple varying actors to portray the character. Not only can it hack computers, but it also gains power to hack humans (kinda like Killgrave from Jessica Jones, but not as sadistic) though Kamala's polymorph nature protects her. The writers could use Doc.X as an allegory for the harm of trolling on the internet, and how it can affect us in the real world. Better still, if there are latter seasons that introduce Stormranger, Doc.X could posses the cybernetic doppelganger as a physical body to challenge Kamala on her level.