Grasshopper mouse (on the top 20 badass list):
The following info is from Wikipedia:
It is a carnivorous rodent, dining on insects (such as grasshoppers), worms, scorpions, snakes, and even other mice. It also stalks its prey in the manner of a cat, sneaking up quietly, and defends its territory by "howling" like a small wolf. The grasshopper mouse is known to be immune to various venoms released by its prey (scorpions, snakes, etc.).[2]
Grasshopper mice tend to have low population densities. They are either alone or in pairs, one male with one female. Very territorial, their average territory size may equal their home range size of about 28 acres.
Their aggressive nature extends beyond their hunting habits, and when held in captivity with other mice, they will often kill and eat those other mice.
