This was a total conversion of Castle Wolfenstein by Andrew Johnson and Preston Nevins
While game mods existed before this both in official form (e.g. Boulder Dash, Pinball Construction set) and unofficial (e.g. Wizardry Scenario Editors, Ultima Editors) this is still considered to be one of the first total conversions with graphics, sounds, and in-game items all changed to fit into a [smurf] mythology. The player assumes the role of Smurfbutcher Bob, captured at the end of the first game in the (unfinished) trilogy, Dino Smurfs. Using rifles and weapons such as smurfberry bombs, you need to escape the castle. Gameplay is essentially the same as Castle Wolfenstein.