When Winston Zeddemore was contracted as a civilian expert for the International Space Project, an unidentified object drifted near the space station. A Major ventured outside to investigate and was attacked. Upon being pulled in, the Major's body was gone and the ghost entered the base.
The rest of the Ghostbusters and Slimer volunteered to go up to the station and investigate the disturbance. As they entered, Egon noticed the ghost's sudden surge in ambient plasmatic energy readings caused external communications to jam. Cut off from Earth, they soon found Winston. He observed the ghost absorbs energy gaining power from living beings' life force like a storage battery. Egon added that if the ghost uses up all the energy, then the victim dies permanently.
Egon and Ray tracked the ghost to the Storage Bay. As Egon witnessed Ray getting absorbed, he realized it was some sort of molecular meld. Unable to fire without damaging the outer hull, Egon was absorbed, too. The ghost then made its way to the Control Room to manipulate the space station to fall back to Earth, where it would escape and have access to unlimited energy: feeding on the life force energy of the entire human race. Peter and Winston were forced to utilize a 20 second Max Boost in order to confine the powerful ghost. As a result, the ghost's victims began to return to their clothes and re-materialize. Meanwhile, Slimer stopped the countdown after bumping into the circuits while trying to find his pet mouse. Just as the Boost's limit was reached, Slimer trapped the entity. It is later seen among the ghosts escaping the Containment Unit when it was opened by Foul Grungy.
Powers and Abilities
The Alien Ghost has the power to absorb a human being then fed off of their life force until it is expended. It can conduct this ritual act on about a dozen at a time, but a limit on how many that could be taken was never specified. It appears to have some form of intelligence as it formulated a plan to crash the space station and escape to Earth.