Milly is a war-tattered wolf of 21 years old. She was friends with Lady Dagger, Mouse KAboom, and Sneaky. She never knew she was with Flippy until she bumps into him a few episodes before the Hide N Seek episode.
She has a severe case of post-traumatic stress disorder (PTSD). Whenever she sees or hears something that reminds her of war (e.g., gunshot-like sounds or crackling campfires), she becomes delusional and extremely aggressive, often killing everyone in sight. (It's possible she also has dissociative identity disorder as a result of her experience in war, judging from her basically becoming someone else in most of her appearances and the few instances she resisted her evil side during Double Whammy and Hear Today, Gone Tomorrow, much like a Dr. Jekyll and Mr. Hyde complex).