The Helper dog is a feature that originated in the MBF source port, created by Lee Killough to demonstrate friendly monster AI. The helper dogs use retouched sprites from Wolfenstein 3D, as well as some of the Wolfenstein dog's original sounds. The dogs are enabled in the MBF port only by use of the -dogs command-line parameter, and they are only available in single-player games (they spawn at the player 2-4 starts). Other ports to feature the MBF helper dog include MBF's descendents, SMMU, Eternity Engine and PrBoom.