Some TMNT stuff really isn't for little kids.
In the Teenage Mutant Ninja Turtles/Ghostbusters miniseries, Stantz and his Ghostbuster cohorts arrived at the scene of a dimensional breach, which had deposited the Turtles, Casey Jones, April O'Neil and Chi-You in their dimension. They attempted to entrap Chi-You, which drove him into retreat along with the humans he had enthralled. The Ghostbusters eventually realized that the Turtles were not demonic creatures, and Stantz took Donatello on a tour of their facility while discussing the supernatural and scientific aspects of their work.
He later accompanied the Turtles to a hockey rink where Chi-You was enslaving humans, and along with Donatello, unsuccessfully attempted to "herd" the immortal into the trap. Afterwards, he and April worked together on a device to free all of the enthralled humans, which Casey Jones set off after Stantz and April were captured by Chi-You. He attempted to free Winston Zeddemore from Chi-You's possession with mood slime, but was knocked unconscious by him.
In Teenage Mutant Ninja Turtles/Ghostbusters 2, Stantz and Egon Spengler were present when Donatello appeared in their dimensional portal, revealing that he and his brothers were being chased by The Collectors. When The Collectors took Donatello, Stantz came up with the solution to take the Turtles on inter-dimensional journeys in order to allow Spengler a chance to come up with a more permanent solution.
Stantz accompanied Raphael on trips through several dimensions, before arriving in a dimensional plane infested with Viking ghosts known as gjenganger. The gjenganger possessed both Raphael and Stantz' bodies, but the pair managed to both reclaim Stantz's body and eventually managed to restore Raphael to his own, using mood slime to expel the ghost.
During the fight, Stantz experienced some of Raphael's memories, and was struck by how lonely and angry the Turtle felt. He was present when the Turtles were briefly reunited with their mother, and she spoke to him about how the Ghostbusters had touched her children's souls.
When The Collectors fought with the Turtles, Stantz and Spengler activated a dimensional gate that led directly into their containment unit, incarcerating them.
- Ray Stantz at Ghostbusters Wiki