Perfuma nearly brings down the Horde singlehanded by simply being herself and driving Hordak crazy in "Flowers For Hordak".
Realizing how desperate Hordak is to get rid of her, She-Ra teases leaving Perfuma behind until Hordak agrees to lift a dangerous spell and give the Rebellion three months of supplies.
Shadow Weaver nearly crushes Bright Moon and the rebellion in a single stroke in "The Crystal Castle". Executing a perfect plan and overpowering Glimmer, Broom and Madame Razz in the process. She-Ra had to cheat with time travel to save the day.
The same episode is also one for Queen Angella, with her castle drained of its protective power and her allies defeated Angella alone managed to hold off Shadow Weaver's assault long enough for She-Ra to save them.
In "The Stone in the Sword" Adora breaks the jewel in her sword protecting the Whispering Woods and can't transform anymore only to discover that Bow has been captured by the Horde. Adora proceeds to climb Sky Dancer mountain and pass several physically and mentally challenging tests to repair her sword, all for the sole purpose of saving her friend. Here, she succeeds in ways Adam never could have.note As far as Teela is concerned, anyway...
Pretty much anytime Hordak and Skeletor face off. Seeing the two biggest baddies of this animated universe go at it in both words and powers is always a joy.
Glimmer holds off Shadow Weaver and a bunch of Horde troopers for nearly an entire episode despite her powers being extremely taxing on her.
In his first appearance, the Sea Hawk charms Adora before finally turning her over to the Horde to save his crew. Sailing off, Swen, his usually meek first mate, speaks up on how bad a move this was.
Sea Hawk: At least, this way we still have our freedom.
Swen: Yes, Captain, we still have our freedom. But...Captain...we've lost all our pride.
Sea Hawk: Mr. Swen? Hard about. Get this ship aloft. We're going back!
Sure enough, Hawk leads his crew to take down the prison transport and save Adora.
She-Ra's transformation in general is awesome, but especially that first time.
Mantenna sums up Bow perfectly: "There's only one man on Etheria crazy enough to attack two tanks on a horse!"
The creators of the show wanted to establish both She-Ra and Adora as bona fide Action Girls, as opposed to the duality of her brother He-Man's MANLINESS versus Adam's (percieved) cowardice. So in Part 4 of the Five-Episode Pilot, while Adora's in Eternia meeting her parents, she gets captured by the Villain Team-Up of Skeletor and Hordak. After a bit of backstabbing from Skeletor leaves her solely at his mercy, she decides to play the Damsel in Distress card by Fainting, "Just like a woman!" Skeletor has Beast-Man, largely considered his most imbecilic subordinate (and that's saying something!), carry Adora to the dungeon...where she promptly drops the act and locks him in the cell in her place.
Beast-Man: "Hey! You can't do this to me!"/
Adora: "Funny...I thought I just did it! 'Bye now!"/
Shadow Weaver gets one in "Of Shadows and Skulls" when she shows what happens to people when she finally gets pushed too far. Summed up, the defeat of Hordak, She-Ra and Skeletor and gets away with it. Of course she also has several others (single-handedly bringing Bright Moon to the brink of defeat, ensnaring all the leaders of the rebellion in a sleep spell and banishing She-Ra to an unknown dimension, wrapping the Whispering Woods in the mist of endless sleep, etc., even defeating He-Man) but that's probably her best episode.
In "The Locket," Hordak takes Sorrowful's new friend prisoner. Sorrowful later rams his head into Hordak's ship and scares him witless.