The Mousers were created by scientist, Baxter Stockman, whom developed the robotic creatures with intentions on solving New York City's rodent problem. The robots are sent after rats and they hunt them down, killing the rodents in their powerful metal jaws. However, this is merely a ruse, as Baxter reveals himself to be mentally psychotic and wants to use the Mousers for evil. His plan is to hold the city for ransom, and if they do not respond to his demands then he will unleash the Mousers to destroy building foundations and force them to collapse, in which he demonstrates on live TV.
April learns of his sinister plan and wants to do something about this. Stockman tricks her into going in the sewers to run for her life, and sends the Mousers there to kill her. April faces certain death until the Turtles appear and rescue her from the metal monsters. Later after April gets to know the Turtles, they plan to storm Baxter's company and put an end to the madness. They confront Baxter and after a battle they're able to stop the Mouser madness.
The Mousers appear in the IDW comic, and are given the name Mousers, because it is short for, "Minefield Ordnance Unarming System Enhanced Robots".
Baxter Stockman is revealed to be Old Hob's benefactor in using him to capture Splinter. After another defeat to the Turtles, Baxter introduces Hob to the Mouser robots. He allows Hob to use them to locate the Turtles lair, and once he does a battle begins. Splinter, Leonardo, and Donatello are attacked by waves on top of waves of Mousers. They manage to collapse a wall on the group leaving only Leonardo to defend against them. Raphael and Michelangelo show up to lend a hand, but the Mousers still overwhelm them due to sheer numbers and Hob quickly learning how to use them.
Michelangelo attempts to save Splinter and get him out of the lair. Hob notices this and sends the Mousers to gang up on Michelangelo. He then uses the confusion to grab Splinter, and then set the Mousers on automatic control. Donatello realizes that Hob isn't controlling the robots anymore; he next figures out how they're able to sense them. He instructs his brothers to file behind him tricking the Mousers into sensing only one Turtle. When the Mousers approach into striking distance, the Turtles attack destroying them all.
The Mousers are dangerous robots that can cause serious damage with their bite. They're not only capable of physically defeating their prey, but they can also chew through brick and concrete destroying walls. However, the Mousers appear to only be as powerful as the mind using them. Since Donatello was able to outsmart them once they were set on auto.