10 Justice League Villains MORE Powerful Than Darkseid
7. Mageddon
Created by Grant Morrison during his JLA run, Mageddon was set up as one of the main villains during his tenure, with several issues leading up to its appearance culminating in the 'World War III' arc at the end of Morrison's time on the series.
A war machine used in the destruction of the old gods, which ultimately led to the creation of the New Gods (including Darkseid), Mageddon had to be exiled and restrained after it had served its purpose, as it was impossible to destroy.
In an apocalyptic fight that required the League to attempt to jump start the evolution of all of humanity, turning the whole Earth into a global Justice League, they eventually managed to defeat the villain at great cost.
Although the character/concept hasn't been revived since, it definitely ranks as one of the JLA's most desperate and climactic battles.