WARNING: The following contains spoilers for Superman & Lois Season 2, Episode 4, "The Inverse Method," which aired Tuesday, Feb. 1 on The CW.
Batman v Superman: Dawn of Justice introduced the DC Extended Universe version of the villainous Doomsday, though the monster met his end at the hands of an equally killed Man of Steel. This wasn't Doomsday's first live-action appearance, and it's unlikely to be the last. In contrast, a recent episode of Superman & Lois revealed that what some fans believed to be the monster that killed Superman was actually another character entirely.
Doomsday has yet to officially appear in the Arrowverse, but he could still return in the DCEU. The villain that fans saw in 2016 wasn't even necessarily the real deal, so whether it's Henry Cavill or someone else, there's a chance that Doomsday could unleash hell once again on the universe that Zack Snyder built.
The Doomsday in Batman v Superman Wasn't the Real One
In Batman v Superman, Doomsday is created as an experiment by Jesse Eisenberg's Lex Luthor, combining his blood with the corpse of the deceased Kryptonian General Zod. This results in a vicious monstrosity with a mutated, inhuman appearance, as well as more monstrous versions of Superman and Zod's powers. Facing him takes the combined might of Batman, Superman and the Amazon heroine Wonder Woman, but even this isn't enough. Sacrificing himself to stop the beast, Superman successfully saves the world, and Luthor himself, from the abomination that Lex had wrought. It's rather ironic that Doomsday was created by Lex's brand of mad science, as this is usually an origin reserved for the corrupted Superman clone Bizarro. Likewise, the character in Superman & Lois that many assumed was Doomsday turned out to be Bizarro, making things even weirder.
This monster wasn't the first of its kind, however, according to director Zack Snyder. He stated that the real Doomsday is still out there and that Lex's creation is not the first of its kind. Material on the DVD release for Man of Steel revealed history about an ancient Kryptonian monster created by a scientist named Bertron. This mirrors Doomsday's comic book origin, in which he's also created by someone with this name. This beast was apparently never killed off and simply discarded somehow, likely mirroring his containment in the comics. Thus, he could easily come to Earth someday and enact destruction worse than what his imitation did in Batman v Superman.
How Doomsday Could Return in Future DCEU Projects
If Doomsday is still just floating in space in containment, it's only a matter of time before he crashes to Earth. To be fair, the Justice League and other metahumans are far more prominent than they were when Lex's Doomsday attacked the Trinity and killed Superman. While the real version might be tougher, the defenders of Earth should have a more fortified defense against him. Of course, there's the matter of where this event would even take place.
The future of Cavill's Superman is highly contested, with the DCEU's continuity in general being in question. Even if Cavill does show up in another movie, let alone a solo Superman flick, it'd be kind of trite to have Doomsday show up again. Instead, with the Multiverse being explored on-screen, it might be interesting to see glimpses set in Krypton's past. This would allow the real Doomsday to be seen in all of his glory, all without devoting too much of another movie to him.
Another idea might be for him to show up at the end of a Superman or Justice League movie, with the combined might of the heroes more than ready to take him on. This would show how the DCEU has evolved from the days when Superman and Batman once slugged it out. Sadly, there's no clue when or if this monstrous beast will land near Metropolis, so Superman may be able to stave off a second death for quite a while.