The first season of Invincible thrived in an era where superhero projects are getting green-lit left and right. It stood out as a non-Marvel or DC property and gave viewers plenty to latch on to throughout its first 8 episodes. While Invincible and Omni-Man emerged as the show's most complex characters, other characters have enough presence to warrant more development in the next season.
By the first season finale, almost every character had some sort of storyline that was implied to be continued in season 2. As the Grayson family will continue to be at the center of the show, the characters surrounding them could have big implications as to how the second season plays out as a whole.
Art Rosenbaum
Every hero needs someone like Art Rosenbaum in their corner. Not only is he the engineer behind Invincible and Omni-Man's costume, but he's always good for a nugget of wisdom whenever Mark comes around.
While he's only appeared in three episodes so far, it's been clear that Art has had a very close relationship with Nolan Grayson and his family. After Nolan killed the original Guardians of the Globe, it was unsurprising that Art was shocked and developed a sense of fear of the person who he had called his friend. In season 2, it would be great to explore more of Art's past and how he became acquainted with the now infamous Omni-Man.
Allen the Alien
In Mark's first trip to space, he encounters Allen the Alien, where they initially fight after Allen mistakes Mark for Omni-Man. After their misunderstanding, they become cordial and Allen explains that he represents the Coalition of Planets. Allen and Mark meet again in the season 1 finale after Allen intercepts Mark while he's going to look for his father.
Mark explains to Allen that his father just abandoned Earth after their fight and Allen is shocked because he and the Coalition of Planets know that Viltrumites like Omni-Man don't give up easily when trying to take over. Future Allen appearances could see him and Invincible team up and provide a good balance of action and hilarious quips.
Debbie Grayson
As the only fully human member of the Grayson family, Debbie was shown to always be there for Mark and Nolan. Debbie did appear in every episode of season 1 but she was significantly less developed as a character compared to the rest of her family.
In season 2, there will be plenty of opportunities to explore her character more after Nolan left Debbie and Mark alone on Earth. Debbie is a good mom to Mark and provided the backbone and support he needed when he wasn't getting it anywhere else. Now that it's just those two, fans are more than likely going to see more of her character and how she moves forward without Nolan.
Titan
Titan as a character is grounded in the fact that he resorts to morally questionable actions to take care of his wife and daughter. Especially before meeting Invincible, it seemed as if Titan wanted to live a regular life despite having powers that encase his body in rock. But after he, Invincible, and the new Guardians of the Globe team up to take down his boss, he takes over as the new leader of the crime organization.
It alluded to that in season 2, Titan will have a bigger role. Considering he is in a new position of power and has intentions of making the city better (in his words), it will be interesting to see how he goes about doing so and how he performs as the new leader of the underworld.
Damien Darkblood
Arguably the most mysterious character from season 1, Damien Darkblood is a demon detective that helps Cecil and the Global Defense Agency try to solve the massacre of the original Guardians of the Globe. After moving forward with the case despite Cecil's advice to drop it, he gets sent back to Hell after Cecil reveals he knows that Omni-Man was behind the massacre but wants to know his motivations.
After Damien's banishment back to Hell, the probability of a return in season 2 is up in the air. Should he return, he deserves some sort of redemption after being the first to suspect Omni-Man as the killer of the Guardians of the Globe. The character was always great for raising the level of tension in every scene he was in and that demonstrates how he could be utilized moving forward.
Monster Girl
Amanda (AKA Monster Girl) has some of the simplest powers of the new Guardians of the Globe, but they come with one of the more intriguing stories behind them. She's able to transform into a powerful monster on command, but it comes with the side effect of her de-aging human form and giving her the appearance of a child despite being 24 years old.
Her powers more than likely directly affect how she operates in her daily life, which would be an interesting storyline to explore in season 2. While the other Guardians of the Globe can put their powers to the side while they live their lives, Amanda does not necessarily get to enjoy that luxury.
The Immortal
The original Guardians of the Globe were all capable superheroes, but they didn't stand a chance against Omni-Man, who is leagues more powerful than they were. The Immortal was the only one able to put up a solid fight against him, but both times they faced ended in his death.
As viewers have seen, The Immortal has lived up to his name so far, as he's been resurrected and seems as if he will be resurrected again as of the season 1 finale. A third fight with Omni-Man would most likely end in another loss for The Immortal, but their matchups have been fairly entertaining and would represent how the public perception of Omni-Man has shifted since their last fight.
The Mauler Twins
Though they weren't the main antagonists of the first season, The Mauler twins were present enough to have a solid impact on the first season as a whole. They're the first villains seen in the show and are even responsible for the most recent resurrection of The Immortal.
The Mauler Twins are technically the same person but cloned, and it's never clear to which one is the original. Despite this, they're still presented as some of the more intelligent beings within the first handful of Invincible episodes. By the season 1 finale, they were arrested once more, but viewers shouldn't be surprised if they plan another prison breakout and have an elevated role in the next season.
Robot (Cloned Human Form)
Robot had a lot of screen time in season 1 as the leader of the new Guardians of the Globe. While he led the team, his main mission of creating a new human body for himself was something he hid from everyone. As viewers saw his bronze mechanical form for the majority of the season, his new human form was only seen for a few minutes in the finale.
Robot is canonically 30 years old, and the new form is a clone of a younger version of Rex Splode, allowing him to transfer his consciousness into a human body for the first time since his first form which predates his mechanical body. Despite Robot's genius, he'll probably need some time to adjust to his new form and his implied new relationship with Monster Girl.
Conquest
While Conquest appearing in season 2 isn't a stretch, his "blink and you'll miss it" cameo in season 1 should get fans excited for what's to come with the character. He only appears for only a few seconds during Omni-Man's Viltrum flashback while explaining his true mission to Mark. Conquest is one of the most powerful Viltrumites and even in his few seconds of screen time, he looks menacing.
Considering how Invincible is adapting its comic storylines, the character may not appear again until late in the next season or until season 3 but the Conquest story arc is definitely something that the show is hinting at exploring in the future.