After that, everyone more or less knew what happened. Following Blackest Night, the Little Blue Men of Earth-0 planned to use Parallax's energy to create a third-generation Lantern Corps and replace Hal and the other disobedient second-generation Lanterns. Little Dai and the others had experienced these events firsthand.
But due to an operational error during the experiment, Parallax, who had endured all manner of experiments for nine hundred million years, escaped.
He had originally looked like a handsome blond, blue-eyed man, but after escaping, years upon years of experiments had turned him into a version of Translucent with glowing veins.
The Little Blue Men had not had a bad idea. Parallax possessed all seven colors of light and was immensely powerful, so using his tissue for cloning seemed reasonable.
But they had not anticipated that every one of those Clones would essentially be Parallax's duplicate, capable of being controlled by him.
Thus, the Guardians were nearly wiped out. Only a few escaped Oa and fled to Earth to seek the Justice League's help.
The Justice League organized an expedition force and struggled desperately until Hal and Sinestro joined forces to summon Nekron, using his control over death to temporarily eliminate Parallax's threat.
Because other Parallaxes still existed on the Timeline, he could not truly be killed. The one who had died was merely Earth-0's temporal fragment of Parallax.
In short, Oa was saved and the Guardians were revived. Then they planned to trap the Justice League expedition force on Oa, because anyone capable of defeating Parallax was simply too great a threat. They figured they might as well try to betray them once.
After all, these people were Superheroes. Even if the assassination failed, they could just throw out one member to take the blame, apologize, and erase the history