The Real Ghostbusters (1986)

S5E11 Trading Faces

A poorly crafted doppelgänger of Slimer unexpectedly bursts into the firehouse through a mirror, causing chaos. In the process, both Louis and the genuine Slimer find themselves transported to the Ghost World. As they navigate this strange realm, they must find a way to return home while dealing with the antics of their ghostly surroundings.