Lycan Mouse
From MHWiki
"Once a passive breed of mouse, when night falls the Lycan transforms into a massive beast that strikes fear into even the most steadfast of hunters. Known to stalk shadowy forests and graveyards, this mouse possesses incredible speed and power. A hunter should be well-prepared before seeking out this adversary.
Capturing this mouse may break its curse, potentially revealing secrets from whence it came."
The Lycan Mouse is a breed of mice found in the Mousoleum and Training Grounds. They are worth at least 5,500 Gold and considered near impossible to catch.
Lycan Mice from the Mousoleum occasionally drop Shredded Furoma Map Pieces, giving Grandmaster hunters access to the Training Grounds.