Spooks Away, a rival company of the Ghostbusters, used a Prediction Engine fueled by entities to see the future and steal equipment before it was built. Since necromancy was involved, Egon Spengler asked Ray Stantz if he could disrupt the machine. Ray slipped a doughnut in it. The control matrix was gummed up and the engine went critical. The entities were combined into one Mega-Entity. It burst out of the Spooks Away Facility. The Ghostbusters opened fire but the streams were ineffectual. It almost smashed Saul Pendleton, the leader of Spooks Away, but Winston Zeddemore tackled him out of the way. It emitted fire next. Egon was sure the key was to break up the entity but wasn't sure how. Ray remembered Slimer was part of the entity. Peter jumped into a jelly doughnut van and enticed Slimer. It worked and he pulled free. The other entities soon broke out and the Mega-Entity was no more.
The Mega-Entity has brute strength, can breath fire, and was impervious to the Proton Packs.
The Mega-Entity is a Class 99.