Goosebumps: Attack of the Mutant Part 1 & 2

Skipper Matthews has an awesome comic book collection. His favorite is the Masked Mutant, the story of an evil, power-mad supervillain who is out to gain control of the universe! One day, while lost in a strange part of town, Skipper discovers a building that mysteriously resembles the Mutant's secret headquarters... a building that magically disappears...