Karone's reintroduction episode. Dressing up as Astronema and using her infamy to stop the auction of and walk out of the Bad-Guy Bar with the Pink Quasar Saber (which the Rangers had lost after Kendrix's death) and creaming everyone in a Bar Brawl when Trakeena exposed her, is just the tip of the iceberg. It was so awesome that the Fridge Logic didn't set in until the Humongous Mecha fight started and the plot stopped. It's a lucky thing that it and the subsequent episode were such great moments for her character, as, combined with the episodes needed to write around Valerie Vernon's illness, there simply was not enough time to really develop her character before the final Story Arc and finale.
Her introduction is great as she makes a perfect bid to assembled hordes: She gets the Saber and they all get to leave with their lives. Her reputation is so great, they just back up and let her have the Saber and she might have gotten away clean if Trakeena hadn't shown up.
Leo saved the entire season with one pivotal come-from-behind-victory. The key to his success? Ripping his shirt off.
Speaking of Leo, in the finale, he was having a bit of trouble finishing off Trakeena for good. His solution? Hold her still and fire his battlizer. At full power. From point-blank range. Even though he knows the explosion could take him out as well.
And then, after emerging from the rubble with his visor cracked, he flashes a weary thumbs up.
Mike becoming the Magna Defender.
"It's time to finish what we started. You will carry on the work we began. My weapon is now yours. You will be the Magna Defender. It is your destiny!"
The last three episodes are filled with Trakeena CMOAs. (Yes, baddies get 'em too.) Suicide. Bomber. Mooks. And that's just one thing.
Villamax cementing his Noble Demon status by refusing to fire on innocent civilians and confronting the newly unhinged Trekeena. Sadly, it was his exit scene, but he did buy the civilians time to escape.
Of course, one of Trakeena's best moments was when Deviot pulled a Starscream on her for the first time. See, last Deviot had seen her, she'd just been Scorpius' bratty daughter, but was since trained by Villamax and Took a Level in Badass. So Deviot sends two assassins to do her in while she's fighting Leo (aforementioned Shirtless Scene)... and she owns them. After killing one of them, she pins the other against a rock with her leg (against its chest or neck, while standing on ground with other foot) and calmly demands to know who put her up to it.
...and then Deviot kills him, pretending to be trying to save her from the attack, before he can talk. Sometimes, his sneakiness could be awesome, too.
Speaking of Trakeena, Deviot and the finale, there's how it begins: After his brief dalliance with the suddenly very dead Captain Mutiny, ol' Deviot comes crawling back to try and weasel his way back onto Trakeena's ship. She refuses to listen and just has Villamax kick the ever-loving crap out of him. After a whole season of manipulation, it's just so good to see Deviot get what's coming to him.
"To The Tenth Power". The first ever full team reunion episode where Deviot gets his hands on the Psycho Rangers from the last season. There's just some great work in the buildup of how strong the psychos are for new fans, and the battle where the teams work together are just awesome to watch.
The moment when the In Space team shows up. At first only Andros appears, teaming up with Leo to save him from Psycho Red. Then in the climactic fight the other show up. It doesn't even matter that how they caught up with Terra Venture isn't explained, or that Zhane is a no-show. It's just that awesome.
Plus, the moment when they morph, the theme for In Space plays, and effortlessly segues into Lost Galaxy's.
The Power of Pink. The first time in the franchise a ranger actually died in the line of duty.
To wit, Psycho Pink set up an attack on Terra Venture that would destroy the colony, using Cassie's space morpher as the power source (slowly killing Cassie as it drains the power from her morpher). Kendrix, the only other Ranger around, walks through several energy barriers, getting buffetted and tossed around by the overwhelming power, and destroys the weapon, getting killed in the ensuing explosion despite saving Cassie and the entire Terra Venture colony. Her spirit then comforts her grieving friends before departing.I'm not crying, you are!
Before that, Psycho Pink, having freed herself from her Restraining Bolt, fires a blast at Trakeena and Villamax effortlessly blocks with his sword.
One of the final moments of the series is one of the most epic, jaw-droppingly awesome moments in the history of the franchise. The space colony (structurally, the ship is a collection of enormous domes connected by tubes) Terra Venture crashes onto the moon of the planet Mirinoi, and the passengers and crew successfully evacuate to the planet below. But they're still in danger - Trakeena, using her new-found power, raises the city dome (what it says, a dome the size of an enormous city) and throws it at the planet below. The Rangers arrive on board the falling city dome, fight and defeat Trakeena. But it's too late - the dome has made it through the atmosphere and is falling straight towards the colonists. From the size and speed of the city dome, the impact will kill everybody there and likely wipe out half the planet, and even the Rangers are panic-stricken and helpless. From out of nowhere, the Galaxy Megazord flies up to meet the city dome, grabs hold of it, slows the dome down and steers it away from the colonists and into an abandoned valley, giving the Rangers time to escape into their zords before the dome crashes. In terms of a power-feat from the Galaxy Megazord, it's astronomical. In terms of sheer epic awesomeness? Mind-blowing.
As far as Rangers fighting with their chief villain go, the last few episodes rank pretty high up there. Trakeena just throws out the Monster of the Week play book after absorbing Deviot into her and throws everything she's got at Terra Venture and the Rangers (one might wonder why she didn't just fire at the very visible engines long ago). Just the first episode in the finale alone has tiny rangers running from her huge starship, and Terra Venture being irreparably ruined. The second episode she rattles her entire mook army and has them swarm the accessory zords (save the original in the moment above) in suicide vests. This is a "Funny Aneurysm" Moment today, naturally, but even The Dragon is alarmed by her recklessness. So she completes her Villainous Breakdown by killing him, too.
Turning a nature-themed Sentai into a space-themed one on top of the behind the scenes disasters and still coming out with a damn impressive final product makes this series one for the production team. Even fans who aren't fond of the season will still applaud them for making it just work.
Special mention goes to the episode "The Rescue Mission," which was essentially "Alien in 22 minutes on a Saturday morning kids show," involving very little morphed footage and no footage from the Sentai. And it is one of the best episodes of the entire franchise.
Oh, speaking of no footage of Sentai bit. It is the first Power Rangers episode ever to have absolutely no Sentai footage (not even Stock Footage) incorporated in the episode, and the only one until the first episode of Dino Charge, aired more than fifteen years after "The Rescue Mission".
Another special mention to "Hexuba's Graveyard" which had a large amount of original fight footage; how large? In the corresponding Sentai episode, the Gingamen didn't actually defeat any of the revived monsters.