Three months later, the band visit a psychic that Cassidy used to frequent to get advice on whether they should finish their album or not. If I went to a psychic and the guy had his face painted like the Joker and was wearing a red union suit with a jock strap on the outside, I would've been out of there. But they stay long enough to get a reading and for Neal to punch the psychic in the face.
They decide the album needs to be completed and head to a recording studio for an all night session. While in the bathroom, Dora gets possessed by a bloody Cassidy. Then she starts wearing sunglasses to hide her green glowing eyes, acts weird, and begins killing her friends. It's all pretty tame since the blood smeared on Dora is the color of red lipstick and the stabbings are not shown on camera.
At one point the camera is behind Dora who is kneeling. She looks up and to the left. Cut to a front view of Dora looking to the right. Sooooo, there are two Dora's and one is Cassidy as Dora's doppleganger? No, it's just bad editing.
The end of the movie is even more nonsensical than the rest of it. Both the psychic and Cassidy show up at the recording studio. Cassidy whines some more, (which the possessed Dora has done throughout the night), and after some more stabbing, she stops trying to kill people and apologizes. Huh?!?