Simplify the following text for a Grade 8 native English-speaking person.
Original: There was also a trilogy of TMNT video games for the original Game Boy system made by Konami , consisting of : Teenage Mutant Ninja Turtles : Fall of the Foot Clan , Teenage Mutant Ninja Turtles II : Back from the Sewers , and Teenage Mutant Ninja Turtles III : Radical Rescue .
Simplified: Teenage Mutant Ninja Turtles ( or TMNT ) are a group of fictional characters .