Superman/Batman: Legends of the World's Finest is a peculiar comic book: its art style is grotesque, its storyline strange and convoluted, and its characters misrepresented. In it, Superman and Batman are plagued by nightmares as the tortured soul of Tullus escapes Hell.
The art style compliments the dread atmosphere of the book, but the storyline's twists and turns sometimes make light of the situation. An example: Batman cannot sleep due to nightmares of Kryptonians dying as his parents did. As he surveys Gotham's streets waiting for a criminal to appear, he is startled by a few rats. When he has calmed down, the criminal shows up, to which Batman tries to apprehend him. Instead of actually succeeding, Batman... trips over some boxes and lets the criminal get away. It is comedic, to say the least, but also not in line with how Batman would usually operate. Similar can be stated about Superman, who turns into a coldblooded, violent vigilante due to his nightmares. It is part of the story that Batman and Superman “switch” personalities because of the demon’s influence, but making Batman afraid of the night is not character development or interesting when his moments of doubt are off-panel.
The villains of this tale, Tullus and Silver Banshee, have an interesting lineage and understandably try to employ Superman to do their dirty deeds, but otherwise offer nothing of substance. Superman turning completely evil under Tullus also does not seem to make sense: because Superman has bad dreams, he becomes evil? Seems like an incredibly large Achilles’ heel.
The resolution of this tale is also rushed and does not seem to resolve the actual problems posed in this comic: what are the implications of Batman and Superman, clear opposites, switching personalities? Do not bother: the question is not answered.