The Mud Pack is the name of a group of Batman Rogues who used the name Clayface, most possessing shapeshifting abilities. Seeing common cause in their battles against Batman, the first Clayface, Basil Karlo, unites all the Clayfaces in the "Mud Pack" in a united effort to rid themselves of the Dark Knight once and for all.
While the first Clayface, Basil Karlo, languishes in a prison hospital, the fourth Clayface, Sondra Fuller, visits him out of curiosity. Karlo proposes an alliance between all living Clayfaces to kill Batman. Basil agrees to join the group, which he dubbed "The Mud Pack".
At Arkham Asylum, an enraged Preston Payne (Clayface III) escapes from his confinement and kills at least one orderly in his escape. Batman is called in from his patrol immediately to help recapture Payne.
Meanwhile, Karlo has been released from prison and is setting up a new base of operation in the abandoned La Scala Theater, casually murdering several muggers attempting to rob him.
Karlo reveales he had gathered the remains of the deceased second Clayface, Matt Hagen, to launch an attempt to revive Hagen.
Payne is surrounded by Arkham security guards who successfully tranquilize him. The asylum guards are confronted by Sondra Fuller, who is posing as the hero Looker. She uses her mental powers to ensnare their minds and tranquilize each other. He then uses her telekinesis to carry Payne away. She then makes her escape with Payne to the abandoned theater where she and Karlo had agreed to make their base of operations.
Karlo, meanwhile, tries in vain to reanimate Matt Hagen. Batman investigates the scene of Payne's escape from the guards, and he finds the mannequin head of Helena that is used to calm Payne in his cell, and also that Payne was tranquilized and he finds that a woman was present on the scene. In looking over Arkham's security footage, Looker was seen to visit Payne that afternoon.
Fuller arrives at Karlo's lair with Payne in tow. Karlo calls the meeting of the Mud Pack to order and establishes the groups discussion points as:
- 1- "How we lay claim to the fame and fortune that is deservedly ours."
- 2- "How we acquire power beyond our wildest dreams!"
- 3- "How we can finally best the caped crusader, whose very existence each of us has every reason to hate."
- 4- "How we will kill him!"
Even though the Mud Pack, as the group called itself, is defeated, Karlo manages, by tricking his allies, to imbue himself with abilities similar to those of Preston Payne and Sondra Fuller. He was defeated by the combined efforts of Batman and the real Looker of the Outsiders by overloading his abilities, making him melt into the ground.
The Mud Pack's origin is even further explored in Secret Origins #44, 1990.