He managed to take out a top level ranger in the very first episode! Himself!
The Rangers had to get awesome multiple times just to beat Koragg. In the final zord battle of Stranger Within, the Titan Megazord takes to the sky and channels the spirits of the ancient Titans into its finishing move. The blast leaves Koragg lying defeated in a pile of rubble. For the first time that season, Koragg leaves not because he's tired of fighting or because of his own hang-ups, but because he's genuinely beaten and has to retreat to save his life.
In her first appearance, Udonna morphs into the White Ranger to fight a twenty-foot-tall forest troll as it tears through a woodland village, easily dispatching it as the Rangers watch on, speechless.
Nick riding out of the portal on Catastros and forming the Centaurus Phoenix Megazord, making everyone, especially Koragg, go WTF was nothing short of awesome
Also Nick forming enough resolve to make his magic work in a dimension where good magic does not exist to heal the injured Catastros
Nick got another great moment during the Dark Wish saga. When Koragg approaches the team of powerless Rangers, he throws his sword to the ground, declaring a truce. Nick is having none of that, so he marches forward, grabs the sword in both hands and takes a wild swing at Koragg. He's only stopped when the other four Rangers wrestle him back and talk some sense into him.
Walking through a dark alley, Leelee, who we've seen just a bitchy but otherwise harmless teen, is suddenly attacked by Necrolai. You figure she's dead meat...until she suddenly pulls out some awesome martial arts moves to take the fight to the monster and hold her own. And then you discover the two are actually mother and daughter, shifting the view of Leelee forever and one of the best plot twists in the history of the show.
Oddly enough, Madison being saved from a monster by Frog!Daggeron was kinda awesome.
Madison got a great one-liner during Ranger Down. The team is fighting the Screamer monster, a bird-themed monster who turns people into piles of feathers. Once Madison and Jenji (the team's resident cat genie) have teamed up to defeat the beast, Madison turns to the camera and says, "Scream at this!" as the monster explodes in flames behind her.
After getting de-brainwashed, Koragg/Leanbow's arrival when the Rangers are getting double-teamed by Megahorn and Black Lance. Centaur mode vs. chariot... dude.
The arc of the Ten Terrors gave pretty much the entire cast multiple crowning moments. The Terrors were described as being ancient elder beings who were (mostly) pure evil and unbelievably powerful. In the source material, they were a pantheon of gods. But by the end of the season, the Rangers had all gotten so powerful that this barely slowed them down. Koragg, Nick, Madison and Daggeron all soloed a Terror (Gekkor, Oculous, Magma and Megahorn respectively). Udonna showed up and knocked Hekatoid off his feet during Light Source. Even the team's pet dragon Fireheart got in on the action, delivering a sound thumping to Black Lance in Mystic Fate.
''Light Source part 2' was basically twenty minutes of every character stepping up and being awesome.
Firstly, ditzy ex-villain Leelee, comic relief "troblin" Phineas, and apprentice sorceress Clare sneak into the Underworld to get Udonna back. When they're interrupted by the Terror Hekatoid, Claire uses the invisibility spell (that she'd been practicing, ineffectively, all the way back in The Gatekeeper) and this time, it works perfectly. Later in the scene, Phineas goes medieval on some Styxoids as the others can only watch in open-mouthed awe. Phineas even gets his own battle music as he cleans house. The scene is topped only by Leelee taking out the last one, which had gotten back up without Phineas noticing. For the record, Phineas is the only character in the entire history of the franchise to literally wipe the floor with a defeated opponent.
In the city, the Rangers have been defeated by Hekatoid, who is responsible for kidnapping Udonna (and ends the fight by stealing the team's powers). Nick and Xander retreat to the Rockporium (the music shop where the team works), and Nick erupts with emotion over finally finding his birth family only to lose them. Xander turns back to Nick and hits him in the chest with a few truths, ending with, "We're your friends. We're your mates. Your family." Nick is rattled, and apologises.
Toby returns to the music shop to find the Rangers dejected. He asks them to finally tell him why they've been distracted and dashing off all year long, and the kids finally admit to being the Power Rangers. Chip said this to Toby earlier as a joke, and Toby didn't believe him. He doesn't believe them this time either, but instead, inadvertently provides a plan which enables the Rangers to beat Hekatoid.
Let's not gloss over that last point, either. Each one of the Ten Terrors has been monstrously powerful, but the Rangers confront Hekatoid and dogpile on him, unmorphed, using their acrobatics to dodge and avoid his attacks ... all just to tire Hekatoid out, allowing Nick to leap in and grab the jar containing their powers.
And we come to the best part of the episode. The Rangers regain their powers, but they're too late to stop a storm of poisonous toads from falling out of the sky to destroy the city ... when the shower of toads freezes in midair with a blast of ice. Leelee, Claire and Phineas's rescue attempt earlier was successful, and the White Ranger appears in front of the team, knocking Hekatoid on his butt. At which point, the team morphs, and for the first time this season, all six Rangers fight together, combining their powers in one epic blast to destroy Hekatoid, and it is glorious.
In the same episode, two Styxoids get genre-savvy: one wishes he could go fight, the other talks about how the ones who do never come back.
Unmorphed Daggeron defeating Imperious... if you can buy it, considering how powerful Impy's been shown to be at other times.
The Gatekeeper sees the gate to the Underworld rise, demonic powerhouses break free, and Morticon (the early Big Bad) rampaging through the city. The Rangers confront him in their zords, and end up totally beaten. They collapse to the ground, powerless, helpless and totally overwhelmed. Madison murmurs softly, "Is this really how it ends?" to which Nick sets his jaw, looks up and says, "No."
From the same episode, Claire versus a suped-up Necrolai, though she did need her mother's borrowed power to do it. And the vampire queen was curbstomped. Claire ends the episode with a monumental feat of power, single-handedly managing to shut the Gateway and send it back underground.
Speaking of Claire, she even managed to go toe-to-toe with Koragg singlehandedly. Though Koragg being who he is, he still won.
And during the climax, the Rangers confront Morticon in the Megazord, and have an almighty battle through the city streets. As Morticon rages, the Megazord receives a sudden power boost, freezing Morticon's evil magic. Udonna, who at this point is trapped in the Underworld, has regained control of her snow staff, and manages to channel her power up into the Megazord. With a giant spectral White Ranger standing behind the Megazord, the Rangers charge up their sword and annihilate Morticon with the theme nusic playing in the background. The entire scene is pure, undiluted awesome.
How can you talk about the episode Gatekeeper, without mentioning Nick fighting against Koraag alone, and after getting beat down, he invoking Heroic Second Wind and kicking Koragg's ass, with the finishing move that defeats Koragg being Nick using a spell to root Koragg's legs into the ground and then doing a Diagonal Cut right though Koragg's sword and onto Koragg. And then he rides Catastros again
Bonus points for Koragg for surviving that attack.
In "Scaredy Cat," Imperious grows far larger than the Megazord and kicks the Rangers around (his CMOA), so Jenji matches him for height and takes him on.
Jenji: Whose the big cat now? What's in my hands? Imperious: Foolish cat! Jenji: Wrong! (opens hands) Power Rangers! (Megazord slashes Imperious in the face and sends him crashing)
In Mystic Fate, once the Master returns, he immediately begins wiping out anybody who could oppose him. At one point, he shows up before the Rangers, drops the dead bodies of their team-mate Daggeron and Nick's father Lianbow at their feet, laughs, and leaves. At this point, Nick gives up. He has no idea what to do, is completely and totally out of ideas. To which Madison, the meek and soft-spoken Blue Ranger, turns to Nick and tells him, "No. You are our leader. You will not give up." Which leads to...
Nick versus the Master in the finale, after the Master has killed just about everyone who could've possibly stopped him. Firass Dirani just killed it in that line
Nick: Not here... NOT NOW ... THIS IS NOT OUR END!
The final battle, when the citizens of Briarwood join hands to restore the Ranger's powers. Their belief in their heroes manifests itself as almost unlimited power, and as they chant, "We believe in magic!", they back away, the theme music kicks in, and the camera pans back to show all eight Rangers with their powers restored, invincible and unstoppable.
And years on, that morph is still seen as one of the best morphs in the entire franchise - including team up morphs.
The flashback showing the Mystic Mother, AKA, the reformed Rita Repulsa. A short bit, but she truly owned it and she conveyed so much with her meager handful of lines.
She was also able to outwit the Master, despite the fact that he'd seemingly killed her earlier. There's a reason she's the Mystic Mother, big guy.
Nick's Big Damn Heroes moment in the second episode. The Rangers beat down the mooks, but Koragg soundly beats them down and is about to finish them off.
Koragg: "Any last words?"
Nick: (out of sight) Yeah!!!
Nick slides inon his bike, leaps from it, knocks Koragg back by kicking on his shield while still unmorphed, and lands perfectly. And then finally uses magic for the first time to block Koragg's sword and knocks him on his ass. And he morphs. Pure awesome
A subtle one in itself. While the other Rangers awaken their magical abilities to fight off mooks, Nick's magical awakening was reserved for the Big Bad's Dragon
Then Koragg summons more mooks and disappears (to qoute: ""fight to another tiem, prove your worth"") Nick singlehandely curbstomps them far worse than his four friends did despite being less experienced than them.
Before Daggeron arrived Jenji's lamp was nothing more than a wishing lamp with a Jerkass Genie. In Daggeron's hands it is a powerful magical blaster who can blast mooks to bits, and its ultimate attack is firing Jenji himself as an attack where he delivers Rapid-Fire Fisticuffs till the opponent is dust
The majority of the Ten Terrors were walking moments of awesome. Its a CMOA in itself that the Rangers survived fighting them, let alone defeating most of them
Imperious gets one in the Dark Wish arc. By being a true Magnificent Bastard. At first he challanges Koragg to prove himself a capable warrior without his mystical powers, knowing the honorable warrior could not refuse it. He then hands the power container to Necrolai for her use, ensuring her loyalty. Then he summons the Barbarian Beasts, extremely powerful and equally dishounourable/dirty/sneaky fighters, and also sharing his hatred of Koragg. He wears out the Rangers by sending one Barbarian Beast at a time to fight them one after another. This leaves the Rangers tired without sleep or rest. When one of the last two of the Beasts is able to reflect any magical attack they use on him back onto Rangers themselves, they use Jenji's special attack, who the other Barbarian beast captures, which was exactly what Imperious was counting on, and uses Jenji's powers to change the timeline so that the Rangers never received their powers.
Koragg got three CMOA's in the same arc:
One of the Barbarian Beasts tries to strike Koragg from behind, but he turns around at the last moment blocks the attack and tells him: "nice try"
A few episodes later, Koragg survives an attempt on his life by two of the barbarian beasts when he was without his magical power and survived, no worse for the wear. He even held his own for a while using nothing but his bare fists after being disarmed while they were using weapons.
And in the evil future he had found and tamed Fireheart. And he uses him to send the Rangers before the magical Tribunal