Some TMNT stuff was always meant for grownups.
Lurch is an amorphous alien blob and an ally to Vanguard. In Teenage Mutant Ninja Turtles issue 12 (Image), it transformed into a female Mutant Turtle and made out with Michelangelo, before revealing its true form and grossing him out.
In Teenage Mutant Ninja Turtles issue 14 (Image), Lurch bound itself with Donatello's cyborg symbiote armor, telling the Turtles that Don was not dead, as had been claimed, but that his spirit was "elsewhere" (the Astral Plane), before flying away.
- Lurch's transformation into the female Turtle was a deliberate finger in the eye to Venus de Milo and her fanbase.