Spoilers follow for Batman Vs. Superman.
One of the Justice League cameos in Batman Vs. Superman featured Cyborg (watch it here) with Victor Stone (played by Ray Fisher) on a slab being revived and brought back to life by some sort of object.
Now it's revealed the object is a Mother Box.
"That’s the first glimpse of the Mother Box there,” director Zack Snyder told EW. “It was an agonizing birth. I really wanted to show Cyborg’s birth because I feel like he plays such a strong part coming up, and I really wanted to give a sense of him. I really want [the audience] to know how far he’s come."
In DC Comics lore, a mother box is a sentient computer that gives its user all sorts of vast powers ranging from teleportation, telekinesis, healing, energy manipulation and more. The Mother Box has been compared to a computer link to the gods and was created by the Apokoliptian scientist Himon the Artificer. In the New 52 comics, Victor Stone is injured by the energy of a Mother Box, with his father Silas using alien tech to save his son, which creates Cyborg.
The Mother Box would be at least the fourth Darkseid Easter Egg in Batman Vs. Superman as the Batman Nightmare scene featured the parademons and Darkseid omega symbol, and it's thought the new Batman Vs. Superman deleted scene features Darkseid's general, Steppenwolf.
The Batman Vs. Superman Cyborg cameo scene also features Cyborg's father, Dr. Silas Stone, a scientist at STAR Labs, played by actor Joe Morton.
"Batman v Superman: Dawn of Justice" has a March 25, 2016 release directed by Zack Snyder starring Ben Affleck as Batman, Henry Cavill as Superman, Gal Gadot as Wonder Woman, Amy Adams as Lois Lane, Laurence Fishburne as Perry White, Diane Lane as Martha Kent, Jeremy Irons as Alfred, Jesse Eisenberg as Lex Luthor, Ray Fisher as Cyborg with Callan Mulvey, Holly Hunter as Senator Finch and Tao Okamoto as Mercy Graves.
Fearing the actions of a god-like Super Hero left unchecked, Gotham City’s own formidable, forceful vigilante takes on Metropolis’s most revered, modern-day savior, while the world wrestles with what sort of hero it really needs. And with Batman and Superman at war with one another, a new threat quickly arises, putting mankind in greater danger than it’s ever known before.