During the franchise's original Mighty Morphin incarnation, the TV show followed a simple weekly formula: Rita Repulsa concocts an evil plot, typically by having her trusty assistant Finster create a new monster, the Rangers stop her plan, and destroy the monster in near-record time. Lather, rinse and repeat that for a successful, enjoyable monster of the week formula.
However, every once in a while, the series would deter away from the usual formula just to spice things up a little bit in Rita's favor. Sometimes, Rita Repulsa's plans would actually work— and on occasion, she would nearly destroy the Rangers.
10 Won: Creating The Green Ranger
One of Rita Repulsa's first successes early into the series came from deciding that the best way to combat the Rangers would be to fight fire with fire. In other words, create a Ranger to destroy the Rangers.
She used her dark magic to create an entirely new Green Ranger and, using mind control, she recruited her own teenager with an attitude named Tommy Oliver. Across a five-part arc, Rita was able to use Tommy to infiltrate both the Rangers' Zords and Command Center, disable Alpha, ship Zordon to another dimension, and even destroy their Megazord. Her new Ranger gave Rita her biggest hot streak of wins.
9 Beaten: Stabbed By Drakkon
Because Rita's mind control was eventually reverted and Tommy decided to join the Rangers, her plan backfired. But in another universe (referred canonically as The World of the Coinless) chronicled in Boom! Studios' "Shattered Grid" storyline, Tommy decided to re-join Rita upon re-gaining his mind.
In working together in this universe, Tommy (adopting the name Lord Drakkon) manages to conquer the world alongside Rita and vanquish the Rangers with ease. However, Drakkon concludes that he wants all of this power for himself, opting to kill Rita with the dagger he gave her when she least expects it.
8 Won: Relieving Tommy Of The Green Ranger's Powers
Although she lost her Green Ranger, she was able to enact revenge on her former pupil by taking away his powers using the Green Candle. When the Green Candle fully burnt out, Tommy's powers would be drained completely.
Tommy giving his Dragon Coin to Jason prevented Rita from receiving the Green Ranger powers directly, but reducing the Rangers line-up to five and even running Tommy out of Angel Grove put a significant dent in the team's armor. In that regard at least, she won in the long run.
7 Beaten: Failed Kidnapping Plot
Some episodes later, during the "Return of an Old Friend" two-parter, Rita Repulsa's latest plot sees her kidnapping all of the adults on Parents Day and refusing to relinquish them unless the Rangers give her their Power Coins.
Not a bad plan by any means, but it proves for naught, especially as it only ends up serving as a vehicle for Tommy to return to Angel Grove with newly charged Green Ranger powers. Even if the charge is temporary, Rita's plot didn't accomplish anything beyond bring her former Green flame back into the fray.
6 Won: Holding The Universe Hostage
In the sixth issue of Mighty Morphin Power Rangers, by Kyle Higgins and Matt Herms, Rita Repulsa is finally able to enact a plan for world domination that she only dreamed of. During an encounter with Rita's energy-depleting Black Dragon, she has Billy kidnapped and uses his Morpher to tap into the Morphin Grid, which she uses to drain the Rangers (except Tommy) of their powers completely.
She is also able to gain control of the Rangers' Zords, using them to threaten world leaders into relinquishing their power to her or risk having their countries destroyed.
5 Beaten: The First Evil Plan
In speaking of the constant monster of the week formula that befell Rita Repulsa time and time again, it is worthwhile to bring up the plan that started it all from the very first episode.
When Rita is first released from her moon dumpster prison, she re-introduces herself to the galaxy by sending Goldar and her Putties to Angel Grove. After being recruited by Zordon, the Power Rangers dispose of them all with ease and sending them back crying to their master. Not bad for a team's first mission.
4 Won: Marrying Lord Zedd
After a brief banishment, Rita returns to the fray with a different kind of plot to conquer the universe. Knowing Lord Zedd is in her way, she finds a way to bring Zedd to her side: By getting Finster to craft a love potion that will force Zedd to fall madly in love with her.
Throughout the second season two-parter, "The Wedding," we see the final seeds of their marriage coming to pass and despite the Rangers' best efforts, they cannot stop the two most diabolical forces in the galaxy from becoming a happy union.
3 Beaten: Rushing Finster's Monsters
When Rita went M.I.A. after her previous defeat at the hands of the Power Rangers, Finster used his newfound free time to perfect his skills as a monster sculptor. While in hiding, he perfected a mechanism that helped his monster disguise themselves perfectly undetected as humans, transforming at random. Littering them across the globe gave the Rangers their biggest challenge yet.
When Rita returned, she spoiled Finster's original plans by forcing him to activate their monster forms all at once and grow them as giant monsters immediately to signal her return in issue #24 by Kyle Higgins and Jonas Scharf. However, because these monsters aren't structurally designed to grow as giants, they weakened easily, allowing the Megazords to destroy them easily and spoil Rita's return party.
2 Won: Killing Off The Original Rangers
Though a box office bomb, the 2017 Power Rangers movie at least gave an interesting alternate backstory for Rita. Rather than being a villain right off the bat, she started off as the Green Ranger before being corrupted by the power which he powers wield.
In a quest to conquer the universe and retrieve the Zeo Crystal, she manages to murder the entire Rangers line-up; except for the Red Ranger, Zordon, who has her sent to the bottom of the sea with a meteor strike to stop her (and kill the dinosaurs, apparently).
1 Beaten: When She Was Purified
In the "Countdown to Destruction" two-part finale to end Power Rangers in Space (and was supposed to mark the end of the franchise as a whole), Zordon sacrificed himself to finally rid the universe of evil. This sacrifice used his last remaining energy to either reduce villains to dust or purify them as pure-hearted civilians. The latter happened to Rita Repulsa.
Sometime between that episode and Power Rangers Mystic Force, it is canon that Rita decided to use her newfound purity to become the Mystic Mother, the Empress of Good Magic.