WARNING: The following contains spoilers for Justice League Infinity #6, on sale now from DC Comics.
The true threat of Justice League Infinity has been quietly risking the entire multiverse while avoiding the attention of the heroes. But now that it's been finally revealed, it turns out to be surprisingly similar to the recent version of Perfect Ultron from the Marvel Cinematic Universe's What If...? -- and turns out to actually be far more terrifying.
In Justice League Infinity #6 (by J.M. DeMatteis, James tucker, Ethen Beavers, Nick Filardi, and AW's DC Hopkins), the true threat to the multiverse is revealed to be an ever-adaptable Amazo robot that has been taken over by one of DC's most terrifying presences.
While confronting the Amazo of the DC Animated Universe and trying to explain to him that continuing to fracture the lines between realities will doom the multiverse, the Justice League are caught by surprise by Overman. The dark variant of Superman was psychically turned into a weapon against Amazo by the unseen presence operating outside of their reality, seriously wounding the android and breaching the barrier between the Justice League and their true foe across the multiverse: a version of the Amazo robot from a different reality. This version of the adaptable creation of Professor Ivo came from a world where the League was never formed, preventing anyone from ever having the chance to teach the robot empathy before the threat it posed became known to the world at large.
Instead, humanity feared Amazo and attacked him -- and the ensuing battle destroyed the world. Slowly, left alone on the husk of the world, the android became a wanderer, destroying every world he found in the galaxy. His last great challenge was the Darkseid of his reality, who had found peace and turned away from his inner darkness. Amazo-II was able to also duplicate the effect of the Anti-Life Equation when the New God attempted to use it against him, and he became a living vessal of the force, fusing with the unknowable and dark consciousness of the incredible power.
This created an even more adaptable and nearly unstoppable creature, who could only breach the multiverse once it had forged a connection with another Amazo. Having located his DCEU variant, the powerful android finally broke free and is now poised to lay waste to the rest of the multiverse by bringing Anti-Life to every reality. It's a massive move by the villain and sets up Amazo-II as one of the most potentially destructive forces in the entire DC Multiverse, possibly exceeding the power levels displayed by the reality-warping Darkest Knight or the recently re-empowered Darkseid.
By gaining this sort of power, even beings like Superman are mere afterthoughts, caught in a psychic illusion in which Amazo-II quickly and effortlessly slaughters much of the Justice League. It's a brutal showcase from the newly enhanced villain, and makes him the ultimate representation of Anti-Life. Other realities such as the world of DCeased have indicated that the Anti-Life Equation is a sentient force of nature. Fused with Amazo, the powerful force has finally gained the chance to spread its influence and destructive power across all of creation -- and potentially the entire multiverse if it's able to succeed in its final mission against the collective Justice Leagues of multiple Earths.