Dimension X is the home dimension of the Kraang in the 2012 series.
So far, it is known that the air of the Kraang's part of Dimension X is nitrogen mixed with sulfur and that it is very foggy. The water of Dimension X has hydrocarbon that can melt anything in the Dimension of Earth. For some reason, the water had no effect on April O'Neil when some of it was accidentally splashed on her. Later revealed to be because she's a human-Kraang hybrid.
"It Came From The Depths" - Leatherhead's flashback shows him being mutated and raised in a Kraang lab in dimension X.
"Booyaka-Showdown, Part 2" - Kraang Prime came to Earth from Dimension X in order to terraform it so the Kraang to live on our dimension.
"The Wrath of Tiger Claw" - Tiger Claw's flashback shows him battling through various dimensions.
"Plan 10" - Raphael takes a glance at the Kraang plans for the invasion.
"Into Dimension X" - It's revealed that time passes faster in Dimension X than on Earth, Mikey gets stuck in there for "months" and Leatherhead gets older after staying in Dimension X for "decades". It's also revealed where the Kraang Power Cell comes from and that a lot of stuff in dimension X reacts to sound.
- Leatherhead (temporarily)
- Michelangelo (temporarily)
- Rock Soldiers
- Sea Monster
- The TCRI episode is the only one to show dimension X's air being green, in every other episode it has a pink coloration to it.