The Phantom Phenomenon - S1-E23
Trivia: So far, the Phantom Ranger is the only Ranger whose identity has never been revealed.
Shift Into Turbo: Part I - S1-E1
Trivia: The original plan for this series was for Lord Zedd and Rita to be the villains for this series, with Divatox joining them later.
Answer: The Rangers are human. Blue Centurion is a robot/cyborg.