The Mouth Critter Ghost is a large ghost with four mouths.
Egon Spengler and Donatello went to the Warehouse to use its ionized glass enclosure to test their Trap-Gate and Proton Weapon prototypes. Egon cautioned Donatello the glass may not be able to withstand too many hints from his Proton Weapon then placed a full Trap into the enclosure's slot and released Mouth Critter Ghost in with Donatello. Donatello asked Egon to humor his request and talk about what it like being dead. Donatello explained talking while fighting was something he did with his brothers and found it comforting. He added he found the ghost terrifying and asked Egon to humor him. Egon replied he experienced a feeling of peace and was able to fully focus on his thoughts then asked Donatello what he meant by his soul being in two places. Donatello explained he was mortally wounded and his consciousness was temporarily placed in a robot shell. He likened it to a dream, sometimes clear and sometimes fuzzy.
Donatello managed to hit the ghost with his proton-powered staff. The ghost retaliated and knocked him across the enclosure. The force and Donatello's shell made a crack in the glass. Donatello decided to try the Trap-Gate. The ghost was concerned at first but Donatello soon realized they miscalculated the power needed. Egon grabbed the Trap but remembered there was a safety in place that kept the door locked to keep any active ghosts contained. He asked Donatello to stall but noticed he sounded like Winston again. Egon instructed him not to let himself drift then asked him to continue with his story. Donatello felt like when he was in the robot, it was him but it wasn't. He recalled his body was hollow but part of him felt warm. Lastly, he remembered being in a garden. Egon ripped out several red wires and unlocked the door. He threw out the Trap and recaptured the ghost. Egon concluded they had to boost the Trap-Gate's power considerably.
- Teenage Mutant Ninja Turtles/Ghostbusters Volume 2