The arcade game didn’t allow much personal creativity from the programmers. All of the enemies are straight from Turtle doctrine, and at most Konami was permitted to devise different types of Foot Soldiers. The NES version let the developers get a little more creative and throw in two extra levels with new bosses: a mutated arctic tiger-wolf-bear named Tora and a robotic samurai named Shogun. Neither of them appeared anywhere else in the Ninja Turtles universe.
There’s another new character who shows up in Teenage Mutant Ninja Turtles II: The Arcade Game, and her presence is never really explained.
In the game’s second level, there's a break in the street brawls against Foot Soldiers. A woman, bedecked in the height of ’80s fashion, rides by on a skateboard. She doesn’t attack or even notice the player’s chosen turtle. If not interrupted, she’ll pass right through the whole fracas.