From the Steam Store page:
Marvel’s Midnight Suns is the ultimate crossover event combining the rich story, character relationships, customization and progression of an RPG with the tactical strategy and combat mechanics of a revolutionary new card-based tactics game. Set in the darker side of the Marvel Universe, you will forge unbreakable bonds with legendary Marvel Super Heroes and dangerous supernatural warriors in the fight against the world’s greatest threat yet…the demonic forces of Lilith and the elder god Chthon.