It appeared in the episode "The Legend of the Kuro Kabuto" when Leo returned to the shredder's lair with the Shredder's Helmet which he used to make a trade with the shredder; the helmet for Karai. the shredder agrees and orders one of The Foot-Bots to bring her up from the dungeon that they imprisoned her in [which surprises Leo]. Leo and the shredder then fight [which the shredder states was going to happen for Leo wasn't going to leave without one]. The other turtles then show up and join in the battle. although they are incapable of defeating the shredder, they manage to distract him long enough to get to the decoy robot [who they think is Karai] and escape [with help from a smoke that they planted in the shredder's helmet before they handed it back to him]. they then carry it to a nearby rooftop and set it down [while revelling in what they just did]. Leo then removes the sack and they all make the shocking discovery. the brothers start to run in different directions [while the bomb countdowns]. The device then detonates and explodes which thrusts them all high into the air [which is how the episode ends in a comic-like style].
It was modelled after Karai's body. The only difference was it's head which was a rectangular bomb and it was deceptively repeated the words "Let Me Go".