Vyperstein is a mod for registered Wolfenstein, made by Scott Vyper. Originally finished in July 2000, it was posted on the Dome on April 25, 2001 in a post that also linked to his website.
The mod features 10 levels, some of which are either cartoon-like or silly in nature. The upside-down guards from Chokage are featured, as is the purple brick texture from that mod, along with other graphics from Schabbs 2000 and Totengraeber.
Though it uses the .WL1 file definition it is not based on shareware Wolfenstein, as all bosses, guards and textures are featured. Other coding changes include new music order and changed episode names.