10 Justice League Villains MORE Powerful Than Darkseid
8. Perpetua
Perpetua is relatively new to the DC universe publishing wise, but was retconned to the dawn of time as mother of all the Multiverse. Created by Scott Snyder for his recent Justice League run, Perpetua was revealed to be the mother of the Monitor, the Anti-Monitor, and the World Forger, having created them to look over matter, anti-matter, and dark matter respectively.
Her work seemingly done, she turns her hand to creating life, devising the 'Apex Predators', the DC Universe's combination of current day humans, and Martians. The Judges of the Source condemned her for this, trapping her in the Source Wall along with her Apex Predators.
After the Source Wall was broken by the Justice League during the events of Dark Nights: Metal, Perpetua was ready to be freed by Lex Luthor and the Legion of Doom.
All this to say, as a being of cosmic creation, and one who ultimately defeated the Justice League at the culmination of Scott Snyder's Justice/Doom War story, Perpetua is absolutely one of the most powerful beings in the multiverse, let alone a dangerous threat for the League.