Mutantstein: The Nightmare Returns is the fifteenth mod by John Bucksnort. It was made in collaboration with Harry Mass Sr and is the first installment in the Mutantstein series. It was released on October 31, 2000.
It features 6 levels and features a new EXE, based on registered Wolfenstein.
An SDL port was released on August 11, 2012.
In October 2019, AstroCreep ported this set to ECWolf, along with the second and third entries in the series.