ClayFighter Xtreme was the working title for ClayFighter 63 1/3, and the original name was kept for the planned PlayStation release, but it was cancelled because Interplay wasn't able to release it at the same time as the Nintendo 64 version, and didn't want it to be perceived as a port of the N64 version. After the N64 version, there was plans to finish the game anyway, but it never happened. If this did happen and the game was finished, it would have been the first (and only) ClayFighter game to be released on the PlayStation.
- Bad Mr. Frosty
- Hobo Cop
- Ickybod Clay
- Dr. Kiln
- Lady Liberty
- Kung Pow
- Zappa Yow Yow boys
- High Five
- Lockjaw Pooch
- Sumo Santa
- On the old Interplay website, the only characters that didn't have a profile were the Zappa Yow Yow Boyz, High Five, Sumo Santa and Lockjaw Pooch, only appearing in the early screenshots of the game. It's assumed they would have been secret/unlockable characters when the game were released.
- There is a leaked beta available of this game owned by the user Mike Mika, who only released a couple of videos of the debug of the game and a preview of Hobo Cop, the cancelled character. Sadly, only this user has a copy of it and seems to have no plans to release it to the internet for public use.
- As said before, Hobo Cop appears as part of this leaked beta. If the game would be completed, there was a chance of Hobo Cop being an exclusive character for this game, since he was removed from the N64 version due to possible controversy, a theme that Sony wouldn't have minded.
- Earthworm Jim was also planned for this game, but didn't appear in old pages. In the beginning, it was said he was added to replace Hobo Cop, but this later was deconfirmed.
- The copy was finally released on April 17, 2021 by the user Stretch The Cow on the Internet Archive, being this user part of Project Beluge, an initiative that want to release on the internet old and forgotten betas from many consoles, included PlayStation, CD-i and Sega Saturn, being ClayFighter Extreme one of those games. The sprites from the characters (Hobo Cop included) were ripped and uploaded to The Spriters Resource, revealing various unused sprites and moves for some characters.