Five Superman villains swear vengeance and wreck devastation on Metropolis to attract him – the entire Justice League arrive but, when the Toyman goes berserk, Superman intercepts a beam meant for Batman and Wonder Woman and is disintegrated. The villains are beaten but the world goes into shock at the death of their greatest hero. The funeral is held but Batman is convinced Superman is still alive.
The League's wake is interrupted by the arrival of Lobo applying for membership. Meanwhile in Metropolis Batman continues his investigation but is interrupted by an onslaught of villains who overwhelm him. Lobo is trying to prove his credentials to a reluctant League with a brawl when they get word of events in Metropolis. With Lobo's help they manage to win . . . while in an alien landscape beneath a red sun, Superman lies unconscious.
Lobo first appeared in the comics in Omega Man #3 (June 1983), and is the last survivor of the planet Czarnia. He claims that he killed everyone else and there's no reason to doubt it. A mercenary and bounty hunter with a rarely-seen affection for space dolphins, he possesses superhuman strength and speed, but most dangerously, the Czarnian ability to regenerate from even a single spilled drop of blood. Every drop of blood becomes a new Lobo, although then they fight it out with each other until there's only one left. Lobo has tangled with many heroes in the DC universe at one time or another.
In the WB animated universe, Lobo was introduced in Superman: The Animated Series, in the episode "The Main Man, Part 1." His origin is not provided there but he is basically still a super-powered bounty hunter with an attitude. He and Superman parted there as more-or-less friends after helping each other out of a jam, but there was no love lost between the two.
Superman Revenge Squad
Although not identified by that name, the Superman villains gathered together are clearly a homage to the Superman Revenge Squad, which has existed in various incarnations (non-super and super-powered) both pre- and post-Crisis and first appeared in 1961. They're plunging a dagger into a table with the Superman emblem mirrors originally the Injustice Society plunging daggers into a map of the U.S. - a scene used in many comics since (such as here), and Legends pt. 2 as well.
As with several Superman villains, there have been several different versions. Pre-Crisis, was crook John Corben rebuilt by an elderly scientist who used experimental techniques to put Corben's brain in a robot body powered by radiation. Corben killed the scientist and figured out he could use green kryptonite to power his body and pose a threat to Superman on that and many other occasions.
Post-Crisis, John Corben was a small-time conman was made into a cyborg by a xenophobic scientist who had acquired a bit of kryptonite and used it to power Corben's body. Corben fought Superman but his kryptonite was stolen by Lex Luthor. He has since found other power sources and acquired greater power by making a deal with the demonic Neron.
In Superman: The Animated Series, John Corbin first appeared in "A Little Piece of Home" as a mercenary who was captured by Superman. In "The Way of All Flesh," Lex Luthor made him a deal - the millionnaire would give Corbin a new kryptonite-powered body to gain revenge. Corbin accepted but soon realized that he couldn't taste or touch and went on a rampage.
In all of his incarnations, Metallo possesses superhuman strength, a robot body capable of absorbing damage, and occasionally the ability to extend and to some degree modify his limbs. He can also fire blasts of kryptonite radiation. This is his first appearance in Justice League.
Livewire is a character unique to the WB animated universe. She was introduced in Superman: The Animated Series, in the episode "Livewire." Radio shock-jock Leslie Willis tried to get high ratings by ranting on Superman, but during a concert she was hit by an electrical discharge and transformed into living electrical energy. Superman defeated her - she later returned to team up with the Parasite, and later still with Harley Quinn and Poison Ivy against Batgirl and Supergirl.
Toyman first appeared in the comics in Action Comics #64 (September 1943). Winslow P. Schott was a seemingly kindly toymaker who specialized in creating deadly toys. This brought him up against Superman, and Schott was clever enough (and had a large enough stock of kryptonite) to go up against the Man of Steel. Later, Schott tried to retire but a new Toyman dressed as a harlequin (the one seen in Challenge of the Superfriends) took on the role. Schott later returned to crime and killed his successor.
Post-Crisis, Schott was reimaged in Superman #13 (June 1988) and was a toymaker in England who was fired. He sought revenge on the company shareholders using toy-gimmicks. Although originally he was reluctant to harm children, he later kidnapped and threatened to kill them. There is also another Toyman, Hiro Okamura, a Japanese boy with a genius intellect, who helps out Superman from time to time.
In the WB animated universe, the Toyman was introduced in Superman: The Animated Series, in the episode "Fun and Games." His origin is basically still that of a demented toymaker, although the exact reason for his bizarre doll-like appearance is never really explained.
The Weather Wizard
The Weather Wizard first appeared in Flash v.1 #110 (December 1959-January 1960). When on his way to prison, Mark Mardon escaped and fled to his brother Clyde's house only to find him dead. Clyde had just discovered a way to control the weather before dying of a heart attack. Mark took his brother's notes and used them to make a wand to generate weather. Mardon began a criminal career as The Weather Wizard, sometimes using his powers on a small scale (such as zapping someone with lightning) and sometimes a larger scale (imprisoning a town in winter), but was defeated by The Flash (Barry Allen) many times. When Barry Allen died, The Weather Wizard went into a semi-retirement until teamed up with other Flash villains Captain Cold, Heat Wave, Captain Boomerang, and Mirror Master. Their death released the demon Neron upon Earth. When there souls were returned, The Weather Wizard and the others went back to a life of crime.
In the WB animated universe, Weather Wizard was introduced in Superman: The Animated Series, "Speed Demons," where Superman and the Flash competed for the title of fastest man alive. Also in that episode, Mark's brother Clyde wasn't dead and Mark siphoned the energy off of Superman and Flash through the monitoring arm bands. With Clyde's help, Superman and The Flash defeated him.