 When the mutated turtles went to the surface world 15 years later in "Rise of the Turtles," they came face-to-face again with the Kraang when they were attempting to kidnap April O'Neil and saved her while her psychologist father Kirby O'Neil was taken captive.In the "Gauntlet," managing to defuse a mutagen bomb placed on the roof of the Wolf Hotel, the turtles learn from Kirby that the Kraang are using various scientists to stabilize the mutagen to their use of it on Earth.But as revealed in "It Came from the Depths," the power cell needed for the Kraang's portal between Dimension X and Earth was stolen by Leatherhead six months prior before they eventually reclaimed it in "The Pulverizer".