Monster Mouse
From MHWiki
"Deep within the bowels of the Laboratory, alone and miserable, lurks a monster so terrifying, so hideous, that no one dares to speak its name.
Known only as Dr. F. Romage's Monster mice, their horrible howls can be heard rumbling throughout the walls of the Lab, haunting those who dwell close enough to hear them."
The Monster Mouse is a breed of mice only found in the Laboratory. They are worth at least 9,100 Gold and considered overpowering to catch.