Some TMNT stuff really isn't for little kids.
The Rat King applauds as a large building collapses, then reflects that it's time for him to go home, since there isn't any life left in this place to interest him. He follows a rat into a small hole in the ground, and emerges in a ruinous stone chamber with a throne and many holes in the walls.
Sitting on the throne, he allows dozens of rats to swarm all over him, listening to what they have to say. One rat particularly intrigues him, and he delightedly crawls back up through another hole, exulting over the "deliciously putrid scent of chaos." He emerges in New York City, much of which is now in smoldering ruins. He commands the rats to run through the city and locate weak and helpless people, declaring that when they think the danger is past, their fun will begin.