Basil Karlo (Earth-Prime)

"Joker's acid flower. Clayface's mud, Killer Croc's tooth. Why you collecting all this stuff from Batman's enemies? So I can succeed where they failed."

- Russell Tavaroff and Black Mask

Clayface was an enemy of Batman and a patient at Arkham Asylum.

Biography
At some point, Clayface became an enemy of Batman before being defeated and locked in Arkham Asylum. Afterwards, Batman kept a sample of his mud in the Batcave until it was stolen in 2021 by "Circe Sionis" and given to Black Mask.