Teenage Mutant Ninja Turtles: Vol. 5: Notes from the Underground

Notes from the Underground - Pt. 1
When Don's examination of some mysterious crystals attracts the attention of a subterranean monster, the Turtles underground exploration unearths a Foot Genetics Lab! A video record of strange experiments reveals more of Shredder's mysterious agenda, but when the mutants attack the boys better watch out, or it's... Everybody out of the gene pool!

Notes from the Underground - Pt. 2
After discovering an abandoned underground Foot Genetics Lab, and after being attacked by once-human Digging Creatures, the Turtles assist those very creatures in trying to repair a Force Field to protect them against mindless beasts roaming the tunnels. But the Force Field needs a new crystal power source, and the only place to get one is by traveling deeper underground, to the seemingly haunted catacombs... where other Diggers have mysteriously vanished.

Notes from the Underground - Pt. 3
After befriending the once-human creatures in an abandoned underground Foot Genetics Lab, the Turtles join them on a journey deeper into the earth where they come upon the ruins of a once great subterranean city. When the Turtles and Creatures start vanishing one by one, only Michelangelo is left - and he finally finds the perpetrator - the city's lone surviving Entity. Though the Entity initially appears benevolent by restoring the creatures to their normal human selves, his true intentions become shockingly clear when he demands that they and the Turtles , will remain in the city forever.