Midnight Suns may not possess a similar roster line-up to their comic counterpart, but they still inevitably have to face the Mother of Demons, Lilith, who had been risen from the dead by H.Y.D.R.A. The supernatural team, spearheaded by Sara/Caretaker and the Daywalker, Blade, reaches out to a few Avengers and other allies to resurrect the key to defeat Lilith, the Hunter.
Assisting the Hunter throughout the story campaign are 12 Heroes from Marvel Comics who represent notable teams and groups, including the Avengers, X-Men, the Runaways, and more. Here's the complete list of playable characters so far, excluding the Hunter, in Midnight Suns.
4th March 2023 Update: We've updated this guide to confirm that the second DLC character, Venom, has arrived to Midnight Suns on 23rd February 2023. He will be available via the Season Pass included in the Legendary Edition and as a separate purchase.
All Playable Characters In Midnight Suns
Each character can join the party by progressing with the story campaign, with Captain Marvel, Blade, Iron Man, and Doctor Strange being the earliest Heroes. Further through the game's progression, other Heroes like the Scarlet Witch, Wolverine, and the Hulk will be available to assist the Hunter much later.
Blade

The half-human, half-vampire "Daywalker," Eric Brooks or Blade, combines the best of both worlds: the strength, speed, endurance, and high senses attributed to his vampire abilities and the inability to burn under sunlight. Favoring a katana as his weapon, Blade mastered several fighting forms to compliment his high-velocity attacks, which enhanced his abilities.
Captain America
Captain Steve Rogers' heart and genetically altered abilities allowed him to serve humanity regardless of the fight he faced. With Lilith beckoning, Captain America happily assisted the Midnight Suns in defeating the Mother of Demons and making him a great ally in combat.
Captain Marvel

Carol Danvers came to the help of the Midnight Suns quite early in the game and continues to provide her abilities and knowledge in and out of the battlefield. While she enjoys a good fight, Captain Marvel is an effective damage dealer, thanks to her Binary state.
Doctor Strange
Responsible for the reawakening of the Hunter, Doctor Steven Strange is the Sorcerer Supreme and Master of the Mystic Arts. Unfortunately, due to the Sanctum Santorium being under attack, he sets up shop at the Abbey, providing much need cosmic assistance to protect the world against Lilith.
Ghost Rider

The Ghost Rider is a long-standing member of the Midnight Suns, with Johnny Blaze being its founder. The character continues to find its presence, with Robbie Reyes possessing the Spirit of Vengeance as he's willing to protect his supernatural family by relentlessly punishing his enemies.
The Incredible Hulk
The last playable character confirmed, Bruce Banner, continuously provides much information and research into H.Y.D.R.A. activities, who are messing with Gamma technology. As his research discovers H.Y.D.R.A.'s actual plans, he brings out the "green guy" to aid the Midnight Suns to stop them and eventually Lilith.
Iron Man

Tony Stark is still the "genius, billionaire, playboy, philanthropist" that we know, but his wealth allows his access to resources that can effectively be useful, like the Iron Man suit. Switching to being a Hero, Stark uses his wealth and resources to change the world for the better, including defeating Lilith before his next board meeting.
Magik
Illyana Rasputin grew up in a rural village in Siberia, but her journey to becoming a powerful mutant occurred at a young age. After being kidnapped and imprisoned in Limbo by Mephisto, her mutant abilities began to form, which allowed her to travel through portals before she became his apprentice and eventually join older brother Colossus at Xavier's School for Gifted Youngsters.
Nico Minoru

Born into privilege, Nico came from a family that prided itself in charitable works until she and the teenage children of various PRIDE members banded together to form The Runaways in the wake of a murder. Nico absorbed the Staff of One after her mother attempted to kill her, thus allowing her complete control of the staff and becoming a practitioner of dark magic.
Scarlet Witch
Wanda Maximoff was birthed with the ability to channel powerful arcane magic, allowing her to seek her true potential and wield the all-powerful Chaos Magic. As she seeks out another famed witch, Agatha Harkness, to control her powers, this apprenticeship ends in tragedy and, subsequently, under Doctor Steven Strange's tutelage.
Spider-Man

Peter Parker was an unlikely ally to the Midnight Suns, who he came to their aid as they attempted to defeat Venom. Before further damage could be unleashed in Manhattan, Spider-Man provided his web-slinging abilities to defeat Venom but took some damage which saw him take up refuge at the Abbey.
Wolverine
As unpredictable and broody as Logan can be, the Wolverine's near-indestructible body and self-healing capabilities make him an unstoppable force. Now fighting alongside the X-Men, he helps out the Midnight Suns in the name of justice and honor.
Firaxis Games confirmed in a developer post on 26th October 2022 that four more characters will join the Midnight Suns for the game's Season Pass. If you pre-ordered the Legendary Edition, you received multiple cosmetics for all Heroes, but Deadpool, Venom, Morbius, and Storm will arrive to the game in future DLCs.
Furthermore, Firaxis Games stated that these DLCs would be launched sometime in 2023, with no confirmed dates. If you didn't pre-order the Midnight Suns Legendary Edition, these DLC characters could be acquired separately, but we have yet to confirm that as of writing.