Knightmare was a lengthy conflict that occurred in a possible future, between Superman's Regime, and Batman's Insurgency, due to the latter wishing to overthrow the new tyranny. Superman would ultimately prevail, however, prompting that possible future's version of the Flash to warn a past version of Batman.
At some point in a possible future, Lois Lane would be killed, with Batman having been unable to prevent it. Consumed with grief, Superman was left susceptible to Darkseid's Anti-Life equation and allied himself with the forces of Apokolips becoming a dark, tyrannical ruler of the planet.  Earth was successfully terraformed by the Mother Boxes and the Regime was founded to aid Superman in his totalitarian Regime of Earth, mercilessly killing anybody who opposes him. Batman promptly founded the Insurgency in order to combat this new threat, thus beginning a long conflict.
KnightmareBatman, in desert clothing, exits a bunker, and watches his Insurgency allies approach. He meets with them and asks for the Kryptonite rock, the only remaining hope of defeating Superman. However, they open the box to reveal only green light bulbs. They apologize to him and hold Batman at gunpoint. He follows through with their commands as the undercover Regime Soldiers reveal themselves to Batman and the Insurgents. They execute them, as Batman watches helplessly.
Angered, he begins a killing spree and guns down multiple stormtroopers, while helping some of his surviving Insurgents escape the area. Although he manages to take down most of the Regime Soldiers while Parademons invade the area and abduct many humans there, Batman is eventually overwhelmed by the remaining stormtroopers there who could barely restrain him. He snaps one of their necks, but then is brutally (but barely) beaten by the other stormtroopers. Seeing the damage that Batman was inflicting on the stormtroopers and their inability to restrain him, a Parademon knocks Batman unconscious.
Batman recuperates chained up in the bunker with his few remaining Insurgent allies, eyeing them helplessly. Superman himself then lands in the bunker, and his Regime Soldiers reverently kneel before their leader. He approaches Batman, swiftly murdering the other Insurgency members with his heat vision. Superman then unmasks the horrified and visibly scared vigilante. He expresses his anger at Bruce for letting "her" die, as she was "his world". Superman gives Batman one final sinister sneer, and ruthlessly kills him by tearing Batman's heart from his chest, thereby ending the conflict.
Batman, not believing this experience to be a dream, initially uses this as an extra justification and motivation in his quest to take down Superman. However, after Superman's death proves Batman's initial thoughts invalid, he finally heeds future Flash's warning, and requests Wonder Woman's assistance in founding the Justice League.
- During Bruce Wayne's nightmare, an Omega Symbol can be seen scorched into the dried up harbor of Gotham City. In the DC Comics universe, this is typically the symbol of Darkseid.
- The name "Knightmare" was not used in any of the films, but is used in action figures and video games to refer to it, and it has since gained widespread media usage.
- The "Knightmare" bears some resemblance to the 2013 DC and Netherrealm Studios video game Injustice: Gods Among Us.
- In the game's alternate timeline, the Joker tricked Superman to kill Lois Lane and their unborn child, resulting in Superman killing the Joker, against Batman's wishes. Superman, full of grief and anger, then became malevolent and established the One-Earth Regime, with him as "High Councilor" and some members of the Justice League (along with "conditioned" criminals) joining his Regime, while others joined Batman's Insurgency against him.
- ↑ Zack Snyder Explains How Lois Lane's Death Leads to Knightmare Timeline
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Batman v Superman: Dawn of Justice
- ↑ Zack Snyder Confirms Fan Speculation: Batman Designed Flash's Knightmare Costume in 'Batman v Superman'
- ↑ Flash Used the Cosmic Treadmill in Batman v Superman, Snyder Confirms