Donatello and his brothers encountered the Foot Clan on a rooftop in New York City, and during the fight he and Michelangelo discussed the things they would like about being human. They witnessed a ninja - whom they nicknamed "Steve" - overwhelm Raphael, though the Turtles were able to defeat the Foot overall.
Later, the Turtles caught "Steve" trying to break into Mason Technologies. Steve morphed and revealed himself to be the Green Power Ranger, Tommy Oliver. His morphing clued the other Rangers into his location, and upon seeing the Turtles fighting Tommy, assumed they were Rita Repulsa's monsters and attacked them.