Complex sentence: Dimension X is a fictional alternate dimension or galaxy in the Teenage Mutant Ninja Turtles (TMNT) 1987 cartoon series, the TMNT Adventures comics, the 2012 series, the IDW comics, and the UK Hero Turtles comics.
Split into simpler sentences: Dimension X is a fictional alternate dimension or galaxy in the Teenage Mutant Ninja Turtles (TMNT) franchise. It appears in various forms in the 1987 cartoon series, the TMNT Adventures comics, the 2012 series, the IDW comics, and the UK Hero Turtles comics.