The Possessed Elevators are high rise elevators possessed by entities such as the Unstable Ghosts.
After Mr. Tummel opened a direct passage to the Netherworld, ghosts infested his building. Some possessed the entire elevator system. When Peter Venkman pressed the "Up" button, all the elevators transmogrified. Unwilling to walk 150 floors up to the roof, the Ghostbusters took a helicopter.
After Janine Melnitz and Louis Tully were kidnapped by one of Poso's Followers, Slimer tried to intervene. The elevator was possessed and snapped at Slimer. It soon vanished once the kidnapping was completed.