Evil Slimer twin is an evil ghost that looks just like Slimer.
Somewhere in the Netherworld, there exists a malignant ghost that resembles Slimer in appearance and appetite. Upon stealing a lollipop from a four-legged young spirit, the evil Slimer twin was accosted by its three older brothers. He happened upon a portal to the physical plane opened via an Antique Mirror purchased by Janine Melnitz at a garage sale.
The evil twin traded places with Slimer and stranded him and Louis Tully in the Netherworld. The twin spray painted the mirror's glass black, which sealed the portal, and threw the mirror away. After returning home covered in slime, Peter Venkman and Egon Spengler became suspicious of Slimer's behavior and Louis' sudden disappearance. They reviewed security tapes and discovered the truth. The Ghostbusters trapped him and saved Slimer and Louis.