He thinks on it the whole time he is escaping from the laughable prison they put him in.
If they can do it, so can he, and he can do it better.
Last time he managed to bring them to the brink of defeat; it was only through the Martian's trickery that they escaped alive.
This time there will be more. More options. More opportunity. More potential.
It won't take much to convince most of those he has his eyes on. Those who hate the Kryptonian alone could suffice, but he has to be prepared to do as his enemies have, and make the possibilities…unlimited.
Sinestro, Sapphire, and Kanjar Ro all hate the Lantern.
Manta will join to strike at the king of Atlantis and any Aquaman considers allies.
Copperhead, Cheetah, Blockbuster, and more can be persuaded with money- the easiest motivator.
After some consideration, he decides not to risk any of Gotham's loose cannons in the line-up. Afterall, Joker and Clayface were the undoings of the Injustice Gang and the Secret Society respectively. But when Fugit comes to him one night, seeking asylum from government pursuers, he can't help but see the Clock King as a potential valued ally.
He could have forced them together. He's been practicing with his powers for months now, despite the dampener strapped to his head in the human's prison. Out in the open, he feels powerful enough now to "push" a small city's worth of people into a bloodletting frenzy of a riot. But he won't leave himself vulnerable again, and it was much easier to personally offer to each and everyone of them a spot on the team.
No. Not a team. An organization. All they need is a name now.
Injustice Gang? Painfully pedestrian, and it doesn't exactly give off the ring of organization.
Secret Society? They will hardly be a secret once his plans get off the ground.
It finally comes to him in another second of thought.
They have to be Legion.