[3] Transdimensional Teenage Mutant Ninja Turtles is a supplement of rules for travel to and adventures in other times and parallel worlds.

Changes to the past (or future) are dealt with using alternate branching time streams (i.e., immutable timelines).

This book introduced extinct animal species, including a wide variety of dinosaurs and Pleistocene mammals.

This book also introduces the idea of mutant humans and features advanced psionic rules.

By sacrificing default human attributes, humans could attain more powerful psionic phenomena, ranging from ectoplasmic arms and legs (to make up for a lack of them) and more powerful mental abilities not previously covered or available in the core rulebook.

In the July 1989 edition of Games International (Issue 7), Paul Mason thought that this book would attract a certain type of player, saying, "If you turned to TMNT because you'd gone through D&D from Basic to Immortals and you were looking for more new gimmicks, then this will satisfy you.

If on the other hand, you turned to TMNT because it was a quirky setting for a game with ample opportunity for extreme characterisation, then you might not be so keen."