A squirrel, mutated by nuclear or genetic means, that has become abnormally large, vicious, deformed or all of the above, and can often be found at Chernobyl or in corny horror videos found on Youtube. Can or cannot be easily killed depending on the grade of mutation. May or may not be zombified.
Chris: Hey did you see that mutant squirrel at the beer bash last night?
Zach: Mutant squirrel what are you talking about??
Chris: No totally man I'm like serial there was like a squirrel and an owl tried to grab it and it fucked up that owl's shit man it ate that owl!!
Zach: Yea I totally missed that. Hey didn't you get high at the beer bash?