Evil Bunny is an assassin sent by the Shock Hopper as punishment once you've started causing problems. She's a deeply fucked up lady and probably the hardest encounter in the game right now. Her cum fucks up your brain and leads to a bad end after a few times. You can get rid of her after the first encounter by selecting a dialogue option saying it was a one-off crazy person, or, failing that, after you've lost to her once, beating her another time will unlock a dialogue option that also gets rid of her. More content for her is planned to be released going forward, but hasn't yet happened, so right now all she does is dog your footsteps and always be a credible threat to killing you, due to things like her massive status resistance, huge pool of shields/hp, and ability to hit through your shields.