Sonic the Hedgehog in Castle Wolfenstein is a mod for shareware Wolfenstein, made by Robert Kalin. The set dates to June 1995, though the attached Read Me sports an April 2002 timestamp.
The mod was never released on the Wolfenstein 3D Dome.
Imagery is taken from the Sonic the Hedgehog franchise. 10 levels are featured, though they are all based on the original levels, with the majority of them simply being remodeled or reduced in terms of sprites and/or actors.
A very old set, it was made for shareware Wolfenstein 1.0 and is thus only playable in DOS.