As well as revealing categorically that Superman does indeed return in Justice League with a psyche-out opening sequence that is revealed to be a dream, the new Justice League trailer has confirmed a theory about Darkseid's Apokolips hordes.
Traditionally, Parademons - the low-intellect henchmen Darkseid uses to do his bidding - were an alien race subservient to the villain whose high tolerance to pain made them useful cannon fodder. They weren't particularly smart or impressive in battle, but they came in huge numbers, which was their chief selling point.
But something changed in the New 52 - and it's that change that has bled into Justice League's presentation of the creatures. When the new continuity launched, the Parademons were reimagined as an army of transformed lifeforms thanks to Apokolipian technology that allowed Darkseid to remold enemies (alive or dead) into the creatures and give them the armour that allows them to fly.
They're transformed sometimes on the battlefield by other specific Parademons that are able to convert captured victims into new Parademons using direct technological infection. And that appears to be what we see in the Justice League trailer, as a human is painfully transformed into the distinctive looking enemy creature.
It's an impactful moment in the trailer, but it does inspire some concerns - not least because it flies a little close to the method of transformation of the gloopy henchmen Enchantress repurposes from her fallen enemies in Suicide Squad. And nobody wants that soert of proximity to a dud, no matter whether it fits Geoff Johns' New 52 story idea or not.
Interestingly, the choice to use that backstory makes it possible that some other elements from the New 52 Parademons are possible. That means we might get to see Parademons that can breathe fire, self-detonate or transform themselves.