Don't Eat the Playdoh

Sometimes comicbook villains are rebooted or reused periodically. Clayface is one of these. The original Clayface was created by Bill Finger and Bob Kane and appeared in Detective Comics #40 in 1940. Originally Clayface was the alter ego of Basil Karlo, an infamous b-list horror film actor. He dressed up in one of his costumed roles, the horror villain Clayface, in order to intimidate, terrorize, and murder people associated with a remake of one of his movies.

The second, and best known Clayface was created by Bill Finger and Shedlon Moldoff in Detective Comics #298 in 1961. Matt Hagen is a career criminal who gets mutated by radioactive material, allowing him to reform and change himself into any shape imaginable. This version of Clayface is the most well known, appearing across most mediums. Later on, the original Basil Karlo Clayface turns himself into a similar transformational monster using Hagen's DNA. There have been 8 other Clayface-related villains throughout Batman's publication history, which seems wholly unnecessary. 

Clayface is an interesting villain, as he is one of the few supernatural villains in the rogues gallery, along with Poison Ivy, and Solomon Grundy. With similar powers to Plastic Man, Clayface is a challenging opponent. Even though this character has seemingly endless opportunities for interesting storylines, complete with a matchup that pits superpowers against Batman, who wins everytime despite no powers of his own, he doesn't have many appearances in or out of comicbooks. There are several animated series where he pops up to great affect, including a very memorable and heartbreaking Growing Pains episode from the New Batman Adventures. He also appears in the Arkham City video game in a pretty substantial role.

Other than that, the character, in my opinion is not used to potential. Clayface's power allows him to turn into literally anyone or anything. He could do similar things to Plasticman, and Mystique from the X-Men, the applications for doing evil, damaging, criminal things could be limitless. I feel like opportunities for this character have been squandered, very much like Bane. Clayface has the potential to be one of Batman's biggest most important foes.