* AngstWhatAngst: Lightning Lad [[spoiler:loses his arm]]. He doesn't mind.
* CompleteMonster: [[ComicBook/{{Brainiac}} Brainiac 1.0]] was a menace from the past who quickly became one of the most dangerous foes the Legion has ever faced. Brainiac 1.0 was introduced in a flashback, where he shrinks and steals the city of Kandor from Krypton. Within Kandor was a power source that was stabilizing Krypton, with this power source gone Krypton was soon destroyed. Brainiac 1.0 himself was destroyed long ago, but [[EnemyWithin his programming resided within Brainiac 5]], cut off from the other systems, [[SealedEvilinACan waiting for a chance to be released]]. This chance came when Brainiac 5 accessed Brainiac 1.0's programming to gain knowledge to defeat [[GalacticConqueror Imperiex]]. Though Brainiac 1.0's knowledge was useful in defeating Imperiex, every time he used it Brainiac 1.0 was able to gain more control. Brainiac 1.0 slowly [[Main/TheCorrupter corrupted]] Brainiac 5, until eventually he [[GrandTheftMe took control of Brainiac 5's body]]. Then Brainiac quickly [[Main/TheStarscream betrays]] [[UngratefulBastard Imperiex (who had helped Brainiac 1.0 take over Brainiac 5's body)]],[[Main/YouHaveOutlivedYourUsefulness killing him because he was no longer useful to him]]. Brainiac then proceeds with his plan to bring the entire universe under his control, [[Main/OmnicidalManiac by transforming all living beings in the universe into streams of data]]. After digitizing some planets, Brainiac returns to his home planet Colu and reprograms all the inhabitants there, so they serve as his army and aid in his quest to digitize the universe.
* DieForOurShip
** Some Timber Wolf fangirls hate Ultra Boy because he's Phantom Girl's boyfriend ''in the comics''.
** Also, some fanfic authors can't stand Shrinking Violet because Brainy seems to like her.
* FashionVictimVillain: Imperiex is supposed to be the BigBad of the show's DarkerAndEdgier season... and he has a silver ponytail that doesn't quite match with the rest of his ensemble.
* FauxSymbolism: The [[spoiler:crown of Kryptonite]].
* FoeYay: Drax's final scene in his episode has him a ''little'' too physically close to Superman for comfort.
* FridgeHorror: It took several hundred years for the Bottled City of Kandor to be released back into the universe as its own planet. Along with Superman's [[LaserGuidedAmnesia memory being wiped]] about him finally saving them, this means that Superman probably died thinking he was unable to keep his promise in the present time.
** Timber Wolf was living in the forests in the form of a beast, Saturn Girl mentions that there were "hundreds of voices calling out for help." Given the fact that Timber Wolf had little semblance of humanity at the time, who's to say that he hasn't been eating his father's experiments in order to survive?
*** Connecting to the "hundreds of voices" thing on Rawl, chances are these were innocent people who were most likely shipwrecked on the planet, wandered around for a bit and found a lone scientist in the forest who was willing to give them shelter and protection from the predators that dwell there, once their guard was down Londo experimented on them and turned them into animals. The worst part? From what we've seen they weren't returned to normal and are stuck living in the wild as animals.
* HoYay: Brainiac 5's fanboy [[HoYay/LegionOfSuperHeroes man-crush on Superman]]. Given an honest-to-gods LampshadeHanging by Timber Wolf in the second season premiere: [[http://www.youtube.com/watch?v=cRxx0oElgpA Behold.]]
* {{Moe}}: Brainy. Website/YouTube commenters can stop talking about how "freakin' adorable!" he is.
* NightmareFuel: "Trials."
* TheScrappy: Cosmic Boy, because he is portrayed as a GoodIsNotNice example of LawfulGood, especially in the second season where he appeared more frequently with {{Jerkass}} tendencies.
* ToughActToFollow: This series was greenlit along with ''WesternAnimation/{{Ben 10}}'' to replace ''WesternAnimation/TeenTitans'', right down to having [[WesternAnimation/TransformersAnimated Derrick Wyatt]] as the head character designer. There's no way it'd be able to avoid comparisons!
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