|This article is about a/an episode in Power Rangers Operation Overdrive.|
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.
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?
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.
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 Vulturus 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' 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 Vulturus. 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. Mack and Bridge team-up to defeat Flurious. Dax, Will and Xander defeat the Fearcats. Rose and Tori battle Moltor and his Lava Lizards, and Ronny and Kira team-up against Kamdor and Miratrix. Tyzonn is able to destroy the newly revived Vulturus and Flurious' 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.
|Mighty Morphin Black Ranger||Adam Park||Johnny Yong Bosch|
|Blue Wind Ranger||Tori Hanson||Sally Martin|
|Yellow Dino Ranger||Kira Ford||Emma Lahana|
|S.P.D. Red Ranger||Bridge Carson||Matt Austin|
|Green Mystic Ranger||Xander Bly||Richard Brancatisano|
- James MacLurcan as Mack Hartford (Red Overdrive Ranger)
- Samuell Benta as Will Aston (Black Overdrive Ranger)
- Gareth Yuen as Dax Lo (Blue Overdrive Ranger)
- Caitlin Murphy as Ronny Robinson (Yellow Overdrive Ranger)
- Rhoda Montemayor as Rose Ortiz (Pink Overdrive Ranger)
- Dwayne Cameron as Tyzonn (Mercury Overdrive Ranger)
- Nic Sampson as Sentinel Knight (voice)
- Johnny Yong Bosch as Adam Park (Mighty Morphin Black Ranger 2)
- Sally Martin as Tori Hanson (Blue Wind Ranger)
- Emma Lahana as Kira Ford (Yellow Dino Ranger)
- Matt Austin as Bridge Carson (Red S.P.D. Ranger 3)
- Richard Brancatisano as Xander Bly (Green Mystic Ranger)
- Rod Lousich as Andrew Hartford
- David Weatherley as Spencer
- Gerald Urquhart as Flurious
- Mark Ferguson as Moltor (voice)
- Adam Gardiner as Kamdor (voice)
- Ria Vandervis as Miratrix
- Kelson Henderson as Mig (voice)
- David Weatherley as Benglo (voice)
- Glen Levy as Thrax (voice)
- Campbell Cooley as Vulturus (voice)
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". 
- This marks the first appearance of Sentinel Knight' Super Form.
- Bridge's Aura reading ability has changed color. When he was the green ranger it was green and now it's red, matching his new color.
- Rita Repulsa, Thrax's mother, became the Mystic Mother in Power Rangers Mystic Force, though Xander strangely did not relate the two together.
- Both Kira and Adam mentioned Tommy Oliver, and how he was a doctor.
- As secondary abilities weren't made commonplace until the Disney era, Adam is the only ranger featured without a special ability when he isn't morphed. Instead his natural karate ability is on display. Adam makes a reference to this fact noting his fighting style is "old school" but it "still gets the job done".
- It is unknown when Thrax was born. It could be possible, out of many other theories, that he was born prior to the destruction of the United Alliance of Evil by Zordon's Energy Wave.
- It is unknown how Alpha 6 ended up on Earth, as Alpha 6 was last known to be on Mirinoi. It is also unknown how his voice shifted from a feminized Alpha 5-like voice to an over-synthesized male one.
- Angel Grove makes an appearance, its first since Lost Galaxy's Quasar Quest.
- Adam receives a new Morphing sequence. Adam doesn't yell "Mastodon" during the morph sequence and he also utilizes a more detailed preparation sequence only seen once before in the season 3 episode Ninja Quest Part I.
- However, in the polish dubbing Adam yells "Mastodon" instead of "It's Morphin Time!".
- Bridge, having changed colors, also received a new morph sequence. It doesn't end with Jack's battle cry ("S.P.D. Red Ranger!") or the pose, instead his stance is more like Sky's when he was morphing into the Red Ranger. Bridge's morph is similar to the Cat Ranger morph, likely due to both (Cat and Bridge's Red) only being used for one episode each and not worth doing the more elaborate morphs of the other S.P.D. Rangers.
- Bridge mentioned Cruger in part 1.
- During Mack and Bridge's battle with Flurious, Bridge tosses his Delta Blasters to Mack. In GoGo Sentai Boukenger vs. Super Sentai, AkaRed, being the embodiment of the Red Sentai Spirit, grants the use of the Delta Blaster's counterpart, the D-Magnums along with weapons of other Sentai Red Rangers, to Bouken Red.
- Adam also seems to have the ability to use the Defender Vest, although it may have been a modification by Andrew.
- During his battle with Thrax, Adam yells out, "Morphinominal!" a phrase coined by Kimberly Ann Hart (Amy Jo Johnson) in the original Mighty Morphin' Power Rangers.
- Kira tells the Overdrive Rangers "I'm sure you'll be back to action in no time", a throwback to battlecry Jason coined in the Mighty Morphin' era of Power Rangers when the rangers would return to battle while partially in their morphed suits, "back to action".
- Adam is shown using Will's hovercycle, keeping in line with the vehicle being built for use by a black ranger.
- During Adam's morphing and fighting sequences. an unnamed soundtrack that used high-pitched instruments was used rather than the "Go Go Power Rangers" theme song. It was believed the reason was due to copyright issues, however this would not have made any sense considering that Disney (at the time) owns the rights to Power Rangers and that technically includes usage of the original theme song as it was heard in the Dino Thunder episode, Legacy of Power. Also, at the end of the second episode, all eleven Rangers put their hands together and called out, "Go Go Power Rangers!".
- It's unclear how Xander knows anything about piloting actual Zords, as the members of Mystic Force themselves transformed into their Zords.
- Thrax's "Evil Alliance" could be a reference towards Dark Specter's United Alliance of Evil (an alliance his parents were apart of).
- This is the first time in the history of the series where another team of rangers pilots the current team's zords.
- Adam, Bridge and Xander were all Green Rangers at one point in time. Xander, however, is the only one of the three who still used his Green Ranger powers.
- Once A Ranger is the fourth team-up in Power Rangers history to feature a combined team of 11 Rangers, proceeded by Power Rangers Zeo/Mighty Morphin Alien Rangers, Power Rangers Lost Galaxy/Power Rangers In Space, and Power Rangers Dino Thunder/Power Rangers Ninja Storm. It is also the second time that Veteran Rangers from more than 2 seasons team-up, the first one being Forever Red, which also commemorates the tenth anniversary of the Power Rangers Franchise.
- The color choices for the team may be a reference to Voltron, including having the black themed ranger as the leader.
- Right as the roll-call starts, usually it's the previous Power Ranger team who goes first then the newest Ranger team does their roll-call, instead the newest team roll-called and the Retro Rangers went second. In the roll-call, however, they all just grunt as they pose.
- Aside from the Overdrive Rangers and Sentinel Knight, Tori is the only Ranger whose Japanese counterpart, Nanami/HurricaneBlue, was in the Japanese counterpart of this team-up, GoGo Sentai Boukenger vs. Super Sentai.
- Moltor, Kamdor, Miratrix, and the Fearcats are the only characters with either direct or semi-direct Boukenger counterparts whose counterparts were not part of GoGo Sentai Boukenger vs. Super Sentai. Only Flurious' counterpart, Arch Priest Gajah, was included in Boukenger's team-up.
- Adam is the only Ranger where no one from his Japanese counterpart's team (Kyoryu Sentai Zyuranger or Gosei Sentai Dairanger, depending on one's point of view) appeared in GoGo Sentai Boukenger vs. Super Sentai (When he originally used the Mastodon Coin, Adam had MammothRanger's suit, but used ShishiRanger's mecha, Mythical Chi Beast Star-Shishi).
- Although Tsubasa Ozu is not Xander's counterpart, Tsubasa's actor Hiroya Matsumoto's counterpart still appeared in this team-up as Nic Sampson/Charlie Thorn voiced Sentinel Knight.
- This is the first time that the series used New Zealand as the country itself when Dax goes back to stunt work in part 2.
- Both this team-up and the Forever Red team-up involved having some type of weapon or villain having to do with Rita Repulsa and Lord Zedd.
- The Sentinel Knight said that he restored the powers of the previous Rangers, however, Xander and Bridge's powers were not destroyed.
- Also note that Bridge is not from this time period so he wouldn't even be born yet.
- This is also the second time Adam has morphed into the Black Mighty Morphin Power Ranger outside of the MMPR era.
- Kira had already met two of the other rangers prior to this episode, although she didn't mention it. Given, she only remembered having met Tori during the Ninja Storm-Dino Thunder team-up, as after both Dino Thunder-S.P.D. team-ups, she had her memory of the events erased, so she didn't remember ever meeting Bridge.
- As with the majority of the season, 'Once a Ranger' received overwhelmingly negative reviews from fans and has even been considered to be the worst team-up of the entire franchise. The main subject of criticism is the fact that the Overdrive Rangers chose to give up their duties as rangers instead of continuing to fight against evil despite losing their powers.
- This is the second and final time Tori is seen helmetless. The other being "Prelude to a Storm".
- When working on the morphing grid Alpha 6 mentions Zordon appropriately asking "What would Zordon do?", a possible allusion to his godlike status in the Mighty Morphin' era of Power Rangers as an alternater version of the phrase "What would Jesus do?".
- Final appearance of the Mysic Force Fighters, used by Xander.
- GoGo Sentai Boukenger vs. Super Sentai - Super Sentai counterpart in Boukenger. See comparison page. (story)
- Task 29: The Golden Sword - Super Sentai counterpart in Boukenger. See comparison page. (fight footage)
- Task. 30: The Rage of the Golden Majin - Super Sentai counterpart in Boukenger. See comparison page. (fight footage)
- Task. 32: The Secret of the Adventure School - Super Sentai counterpart in Boukenger. See comparison page. (Megazord fight footage)