For the first time in cinema history, Superman will face a truly intelligent enemy. Not just another bald businessman with a world domination scheme, but an alien intellect who literally collects cities in jars. Literally.

Source:
@JamesGunn
Who is Brainiac
For those who haven't been reading comics since age eight: Brainiac is one of DC's most powerful and terrifying villains. A green-skinned android obsessed with control, intellect, and destruction. He kidnaps planetary capitals, shrinks them down, and puts them on a shelf.In the comics, he's the one who stole Kandor — the capital of Krypton, Superman's home planet. And Superman's had it out for him ever since, to put it mildly. Now they might finally meet on the big screen — in "Man of Tomorrow," hitting theaters summer 2027.

Source:
dc.fandom.com
The plot in a nutshell
Superman and Lex Luthor (who, based on other Gunn hints, are both in the mix now) are forced to team up against an enemy threatening all of Earth.We're in for something massive and completely different. Gunn doesn't do cookie-cutter. He proved that with "Guardians of the Galaxy" and "Peacemaker." And if he's tackling Superman with Brainiac as the main villain — this is going to be a whole new level for DC films. Earlier, we at zoomboola.com gave you the full breakdown on the development of James Gunn's second Superman film here.