Extreme Ghostbusters
Slimer's Sacrifice (1x23)
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Slimer gets trapped in the containment unit (and Peter Venkman isn't even here to see it), surrounded by some very vindictive ghosts that remember him, including a demon named Surt who wants to bring about Ragnarok. Eduardo goes in to save Slimer, while the rest of the EGB has to bust a demon hound in the Firehouse.