Madonna's spirit is a demonic ghost who once possesses Lisa Simpson and the main antagonist in the comic book Bart Simpson's Treehouse of Horror 2 in the story The Exorsister!.
Although Madonna isn't already dead, her spirit manages to possess Lisa through Madonna's songs in which Lisa is listening to all the time. The entire family soon notices a big change in Lisa's behavior and personality. It first becomes much serious at the party when Lisa spill her lemonade out and then starts singing songs by Madonna randomly.
The possession gets worse and Lisa is now wearing the same clothes as Madonna and imitates her moves and dances. Desperate Marge visits Dr. Julius Hibbert and Dr. Marvin Monroe in order to cure Lisa, only to get several different kinds of diagnosis.
Realizing no doctor knows what problem Lisa has, has only one chance - find an exorcist, as she believes Lisa is actually possessed by a ghost of Madonna. Marge comes to Reverend Timothy Lovejoy and explains him her troubles with Lisa. Although Reverend Lovejoy doesn't believe her at all, he quickly changes his mind when she wants to ask a Catholic priest instead, and he eventually agrees.
After entering Lisa's room, Reverend Lovejoy loses all his doubts - but also confidence and bravery. Lisa is now under Madonna's full control. She sings Madonna's songs backwards, her head is backwards as well (she need to have scapulas forward to be able to wear a cone bra) and she can also float. Terrified Reverend Lovejoy unsuccessfully attempts to use a Crucifix and Bible to evict Madonna's spirit, but then finds a better way - he shows her a negative review of her acting ability and Madonna is forced out of Lisa.
However, Madonna's spirit then possesses Reverend Lovejoy as he leaves the house, forcing him to sing her songs and wear her cone bra as well.