Zack Snyder's Justice League culminates in a massive battle in a deserted Russian city where Steppenwolf has united the three Mother Boxes to form 'The Unity,' which begins terraforming the Earth for Darkseid. The league, now joined by a resurrected Superman in a black suit, fights Steppenwolf and his army of Parademons. In a critical moment, The Flash is wounded, and the Unity synchronizes, causing a massive explosion that seemingly kills the league and dooms the planet. However, The Flash pushes his powers further than ever before, running faster than the speed of light to enter the Speed Force and reverse time by a few crucial seconds. This gives the heroes a second chance. Cyborg, with a supercharge from The Flash and assistance from Superman, manages to get inside the Unity and separate the Mother Boxes. An enraged Steppenwolf is then impaled by Aquaman, punched by Superman, and finally beheaded by Wonder Woman as his body is thrown back through the portal to Apokolips, landing at the feet of a furious Darkseid, who vows to return to Earth for the Anti-Life Equation.
The film's extensive epilogue reveals several key plot points intended for future films. We see Lex Luthor meet with Deathstroke, revealing Batman's secret identity to him. Bruce Wayne has a vision of the 'Knightmare' future, an apocalyptic timeline where Darkseid has conquered Earth and turned Superman into his pawn after murdering Lois Lane. In this future, Batman leads a small resistance force that includes Cyborg, The Flash, Mera, Deathstroke, and, surprisingly, the Joker. The Joker taunts Batman about the death of Robin, and it's implied their truce is temporary as they work to send The Flash back in time to prevent this outcome. The final scene shows Bruce Wayne being visited by the Martian Manhunter, who reveals himself and offers his help in preparing for Darkseid's return.