Some TMNT stuff really isn't for little kids.
The Mousers are robots created by Dr. Baxter Stockman and through this affiliation enemies of the Ninja Turtles. The robots are about knee high. They have a head with sharp teeth and two legs. Their jaws are strong enough to bite through steel.
In the Mirage Comics, the Mousers were originally created by Dr. Baxter Stockman, under the premise of selling them to the government, as a way of fighting New York City's rat problem. However, their creator used them to steal valuables from bank vaults. Later, his assistant, April O'Neil, accidentally stumbled onto Baxter's true intent, to gain billions through theft as he believed himself to be smarter than the authorities.
After April escaped from a secret lab inside Baxter's complex and into the sewers, she was eventually cornered by several mousers. At the last second, the Turtles burst from the shadows and destroy all the mousers. However, April promptly fainted after the turtles showed themselves to her. After waking up in the Lair and calming down from the sight from the Turtles and Master Splinter, she was told of their origins, after that a TV news bulletin came on showing a shadowy figure threatening to destroy a building unless he was paid a ransom. The ransom wasn't paid and the building is destroyed. April Instantly sussed out that Stockman was responsible and lead the turtles to his underground lab. While Leonardo, Raphael, and Michelangelo fought a horde of Mousers off, she and Donatello Initiated an emergency shutdown. It worked and the turtles, along with April, departed from the lab.
Each Mouser was about 60cm. tall, could hold up to five Rats and were controlled by radio waves and were controlled by a central computer.
They would later return in Sometimes They Come Back. In the comic Razorback orders his troops to activate the mousers. Mirage arrives and finds Detective Whitmire within the chaos. He has discovered what’s caused the buildings to collapse, but before he can explain, a swarm of mouser robots erupt from beneath the city streets. Mike finally arrives and the Turtles tell Whitmire to find Trent and get him to safety since he’s the target for the mousers.
The Turtles highjack an ambulance and chase after Razorback’s van. Leonardo climbs on top of the ambulance, chops Razorback’s arm off and then bursts the van’s tire, causing the villains to crash into a dump-truck. All the mousers in Times Square suddenly deactivate, and with good reason: the crash decapitated Razorback (he had been controlling them with a cerebral implant).