Some TMNT stuff really isn't for little kids.
Peter Venkman is a member of the Ghostbusters and an occasional ally of the Turtles in the IDW continuity. He has a PhD in parapsychology and psychology, and is considered the snarky, sarcastic "mouth" of the group.
In the Teenage Mutant Ninja Turtles/Ghostbusters miniseries, Venkman 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. They eventually realized that the "kung-fu Martians" were not demonic creatures, and Venkman introduced the Ghostbusters to their new allies.
He later accompanied the Turtles to the places where Chi-You was enslaving humans, where he assisted Donatello in using a proton pack and used a massive cannon to temporarily disperse the immortal being. Along with the Turtles, he defended the Ghostbusters' headquarters from an incursion, and eventually was able to entrap Chi-You.
He took a more individual role in the Teenage Mutant Ninja Turtles/Ghostbusters 2 miniseries, when the Ghostbusters were called on by the Turtles. Venkman went on an inter-dimensional voyage with Michelangelo in order to stay ahead of the Collectors. They eventually found themselves in the city of Zoo Amsterdam, which was populated by anthropomorphic animals. This included a quartet of Ghostbusturtles who immediately incapacitated and carried off Venkman, mistaking him for an "alien hellbeast." Michelangelo infiltrated their headquarters and managed to convince them to release Venkman.
During this time, Michelangelo experienced an emotional breakdown due to his estrangement from his father, and Venkman both consoled him and gave him psychological advice. He also was present when the Turtles encountered their mother Tang Shen, who was irritated by his jokes.
He served as a distraction for the Darius Dun Collectors, allowing Leonardo to cut one of them in half. When the Turtles left their dimension, he gave Michelangelo a copy of A Beginner's Guide to Psychology.
- Peter Venkman at Ghostbusters Wiki