Once a Ranger

Once a Ranger are the twentieth and twenty-first episodes of Power Rangers Operation Overdrive. They are a two-part special team-up involving Power Rangers from five different generations (collectively known as the Retro or Veteran Rangers) assisting the Overdrive Rangers in defeating a new threat: Thrax, the son of Lord Zedd and Rita Repulsa. The title of the episode is a reference to the long-standing phrase "Once a Ranger, always a Ranger." The episode also commemorates the 15th Anniversary of the Power Rangers franchise.

Plot
The son of Lord Zedd and Rita Repulsa, Thrax, unites all four Corona Aurora-seeking factions of villains into a new Evil Alliance. When they manage to overwhelm the Overdrive Rangers, their connection to the Morphing Grid is severed, and their powers destroyed! With the gems still needing protecting, Sentinel Knight assembles a team of replacement Rangers, made up of members of previous (or future) teams of Power Rangers.

No longer having Ranger powers, the former Overdrive Rangers return to their civilian lives. All but Mack, who learns of Thrax's plans to destroy Sentinel Knight, and seeks out the only item capable of doing so, the legendary sword Excelsior. Will he be doing this alone, or can the call of action prove the adage of "Once a Ranger, Always a Ranger" to his former teammates? Meanwhile, their replacements, the team of Retro Rangers, head to Angel Grove to seek out the only being capable of repairing the Morphing Grid: Alpha 6! Even if they succeed, can two combined teams of Power Rangers stop Thrax for good, and permanently break up the Evil Alliance?

Part 1
Thrax—son of Rita Repulsa and Lord Zedd—is freed, and he recruits all the villains who have been searching for the Jewels of the Corona Aurora—Flurious, Moltor, Kamdor, Miratrix, and the Fearcats Mig and Benglo—to unite with him temporarily. By severing their connection to the Morphing Grid forever, the temporary Evil Alliance destroys the Rangers' powers, and Andrew Hartford cannot fix their destroyed morphers. They use their enhanced skills in an attempt to defeat the villains, but fare no better, so the Sentinel Knight recruits five Rangers — Kira Ford, Xander Bly, Adam Park, Bridge Carson, and Tori Hanson—to replace the Overdrive Rangers until their connection to the Morphing Grid is restored.

Part 2
The villains in Thrax's "Evil Alliance" are angry, because Thrax did not think there would be more Rangers. Meanwhile, Mack Hartford is searching for information on the sword Excelsior—which Thrax says is the only thing capable of eliminating the Sentinel Knight. He tries to retrieve the sword, but is confronted by Thrax, who intends on saving the legacy of his family of Evil. He is unable to claim the sword for himself, so he sends a giant monster named Vulturas into the city to destroy it. The Retro Rangers head him off in the DriveMax Ultrazord and Flash Point Megazord, but are overpowered, and DriveMax Ultrazord loses an arm in the battle.

Meanwhile, Mack convinces the Rangers that they will always be Rangers, powers or not, and they all attempt to free Excelsior from the Warrior-Goddess's hands. The statue comes to life and gives them the sword, sensing the shared friendship and combined conviction in their hearts. Then, Mack heads to the battlefield, where the Retro Rangers are about to be destroyed, and uses the sword Excelsior to destroy Vulturas. Meanwhile, Adam reactivates Alpha 6 and teleports him inside the Morphing Grid, where he fixes the severed connection, restoring the Overdrive Rangers' powers. Mack hands Sentinel Knight the Excelsior sword, which gives the Knight a Cyborg form.

Confronting the "Evil Alliance", all 11 Rangers morph and battle the villains. Adam battles Thrax. Bridge and Mack team-up to defeat Flurious. Dax, Will and Xander defeat the Fear Cats. Tori and Rose battle Moltor and his Lava Lizards, and Kira and Ronny team-up against Kamdor and Miratrix. Tyzonn is able to destroy the newly revived Vulturas and Flurious's Chillers. To finish the battle, the Sentinel Knight arrives in his Cyborg form and destroys Thrax, and then joins the Rangers in defeating the rest of the villains.

Production
Jackie Marchand has said the episode was difficult to create, as they needed to balance between the action, the drama, and the returning cast with the Overdrive team. There were some extra scenes to explain why the Overdrive team is quitting, which were cut from the episode: Marchand says the aired version "didn't reflect well on the Overdrive team and made them seem like assholes".