You will Watch TMNT Season 1 Episode 15 online for free episodes with HQ / high quality. Stream cartoons TMNT 115 Notes from the Underground, Part 3 The source of the mysterious crystals found in the lair appears to be an ancient subterranean city. This site is also the location where Donatello and the Turtles’ monster allies disappear. The city is inhabited by the sole survivor of an ancient race; although he claims wanting to return the creatures to their original form, his true intentions remain unknown. Entity makes his first appearance in the show.