Every season of Young Justice brings a new depth to the world, and what started as just a small team of former sidekicks has sprawled out into a universe of intergalactic politics and generations of super heroic struggle. From the start of the series, Young Justice grappled with multi-layered plots involving many villains who end up being as interesting as some of the heroes. Since the villains are seen so much more briefly than the heroes, they are shrouded in far more mystery, and their plotlines aren't always resolved. If any five villains deserves to come back, its this quintet.
Lobo
Lobo is probably the easiest entry as he's so easy to weave into lager plots. Often hired by the real villains, the intergalactic bounty hunter has made memorable appearances in two episodes of the series, leaving an undeniable impression on audiences. When he first appeared, he was hunting a Krolotean, smacking down Wonder Girl in the process and stoking the fears of alien intervention throughout the world. In his second appearance, he came for Forager and proved how deadly he was when he took on a whole team of heroes at once.
What is most intriguing about Lobo is the creators' spin on the character, toning down his Deadpool-esque qualities in favor of making him a more serious threat. Seeing him take a larger role beyond one-shot appearances would be a delight, and given how unique the creators have made him, there's no doubt they can give him an engaging backstory.
Match
There are so many characters in Young Justice that it can be hard to keep track of them all, especially the ones that haven't been seen in a while, like Match. Cloned to be a "match" for Superman, the Kryptonian clone was considered a failure because of his instability and unpredictability. More powerful and way more violent than Superboy, the more "successful" version of the same experiment, Match is a force to be reckoned with.
Thus far, the team barely reckoned with him at all. When he was last seen in the show, Superboy required the use of his full Kryptonian powers to be able to beat Match. In the comics, he briefly escaped, only to be put back under Lex Luthor's care yet again. If Lex takes a larger role in the next season, then Match could grow into a full on Bizarro to aid his plots.
Despero
Periodically popping up in imprisoned cameos ever since his first appearance, the creators could not be teasing a Despero comeback more if they tried. Prominently featured in his debut episode "Cornered," the intergalactic gladiator was built up as a big league threat from the start. In fact, his entire purpose in coming to Earth was originally to fight the Justice League to test his might against the planet's strongest heroes. Since they were offworld, he settled for the next best thing.
What made his fight so delicious is that he was on a whole other level. After disposing of Captain Marvel with little contest, Despero proved to be far more of a match than anyone else on the team were ready for. His psychic third eye could paralyze its targets and kept the fights "fair," weeding out non-physical threats. However, when it was turned back on him, he never got the chance to declare himself champion. Since then, he's been stewing silently, and fans eagerly wait for a wild rematch.
Black Beetle
In stark contrast to Despero, the main villain of the second season, Black Beetle, had the opportunity to wail on the team time and time again. In almost every clash, he was an overwhelming physical force. In fact, it was only because of his doomsday device that a member of the team was forced to make memorable sacrifice. For that, he may be the villain to strike the biggest blow against the heroes since the show began.
Notably he has not been seen since his retreat into space. Although the scarab that granted him his team-busting power is now lost, it's entirely possible he could find or forge a replacement. Even if he does not, leaving such a major antagonist free to lurk in the shadows can never be good, and fans deserve some closure where he's concerned.
Black Spider
Not every villain can be a big bad, and at the end of the day, the henchmen are just as important as the mastermind. To that end, the assassins of The League of Shadows are a smorgasbord of great henchmen, with a never ending array of assassins with unique takes on the familiar archetype, like with Black Spider. Though little is known about him, it's hard not to see the Spider-Man similarities within Black Spider.
The character has many different versions in the comics, and Young Justice paradoxically finds their unique take by making him a sinister version of Marvel's web-slinger. With the same powerset and a more twisted sense of humor, Black Spider promises to be a lot of fun. With the next season on its way, it would be great to see Black Spider return.