The Mark Grayson fended off his father, Omni-Man, from moving forward with plans to conquer Earth. While the planet is currently safe from Omni-Man, the Invincible finale teased multiple villains that will be part of Mark's future.
The threats set up for Invincible season 2 range from crime bosses to intergalactic armies. The season 1 finale showed the Flaxans, the Sequids, Titan, Doc Seismic, Battle Beast, and the Mauler Twins in a closing montage. There was even a sign that Cecil Stedman could become more of a villain. Meanwhile, the episode also teased that other Viltrumites could come to Earth to finish the job Omni-Man couldn't. All of these foes are expected to be part of Invincible season 2 and make Mark's superhero life quite busy. However, it was the quick scenes featuring the Mauler Twins that appear to set up the perfect villain for Invincible's sophomore season.
Invincible's finale shows the GDA arrest the Mauler Twins again after they burn the warehouse that contained their cloning and mind-transfer technology. The closing montage puts the giant geniuses back in prison for the first time since Robot helped break them out. If Invincible follows the comics, then they might not last long in this familiar location. Kirkman's original version of this story saw Angstrom Levy free the Mauler Twins from capture and recruit them to help his cause. Now that they are back in prison again and Kirkman has teased Levy will be seen in future seasons of the show, Invincible appears to have already set up the perfect next villain for Mark.
Angstrom Levy is a genius and one of Mark's greatest villains in the pages of Invincible. He's introduced as a character from another universe, one where Mark sided with Omni-Man to take over Earth and became a ruthless member of the Viltrum empire. However, another universe's Angstrom Levy then appears to save him and reveals a safe place where hundreds of different Angstrom Levys reside. This is part of the main Levy's plan to gain the knowledge and experiences of every version of himself across the multiverse. He recruits the Mauler twins to build him the technology that can make this idea a reality and becomes hellbent on stopping Invincible when he interrupts the experiment, leaving Levy with severe injuries.
Angstrom Levy's conflict with Mark continues after that, but that would get too far into spoiler territory. Still, he is a distinctly different villain for Mark to encounter in Invincible season 2. Angstrom Levy does have some enhanced physical abilities, but the threat he poses to Invincible is more intellectual than physical. Mark can easily overpower Angstrom Levy unlike Omni-Man, but Levy's plans and methods of gaining power over him are very different. Invincible season 2 going right back to another physically challenging foe for Mark after Omni-Man could feel repetitive, which is why an intellectual foe with multiverse ties like Angstrom Levy is the right direction to go now.