Faceless Eye: The Eye of Thundera lives up to its name; the red cabochon develops a glowing white slitted pupil when it sends a vision through the Sword of Omens, and is sometimes depicted with a black chatoyancy in its resting state.
Face Palm: Lion-O at Tygra's actions after he accidentally drank a love potion meant for Pumyra.
Panthro's frequent reaction to the antics of his teenaged companions. "Oh brother!"
Facial Markings: Used with the Cats to highlight their eyes, cheekbones and jaws.
Famed in Story/Shrouded in Myth: The Sword of Omens, The Eye of Thundera, The Book of Omens, Mumm-Ra and Lost Technology all play important parts in Thunderian legend, but their history is so ancient that Thundera has inevitably forgotten parts of it, and remain skeptical or dismissive of others.
Fan Service: Much of the officially released concept art and character sheets feature main characters in various states of dress and undress. Since the pilot of the original series had all of the leads stark naked, this may be a nod to tradition.
It extends even further in the animation itself,. "Recipe for Disaster" has two scenes that are lifted directly from the opening of the 1985 series.
Fandom Nod: In "Between Brothers", Panthro shouts "I don't need a stinkin' nursemaid!" at Snarf, which is the role he played in the 1985 series.
Fantastic Caste System: Word of God splits Thundera's Cats into two types. Those without tails are society's elite, while those with tails are consigned to a life of poverty in the slums. The Thunderkittens, who have tails, are introduced as pickpockets on the streets. Among the tailless, the line of royal succession is reserved for Lions like Claudus and Lion-O.
Fantastic Drug: Played with the Ro-Bear's Candy Fruit. It's tasty, nutritive... and made of pure sugar. Wilykit and Wilykat quickly become hooked to it and for all means and effects, they behave as if they were eating a cocaine/amphetamine combo. Both purposely get high on Candy Fruit to achieve Caffeine Bullet Time.
Fantastic Racism: By way of Animal Jingoism. A hapless Dog is beaten and mugged by vicious Alley Cats in the slums. At a large festival, Lion-O very narrowly averts a public lynching of two stockaded Lizards, who the Cats enslaved for the crime of petty theft.
In "The Pit", the Dogs don't think very highly of Cats, believing them to be disloyal creatures. Pumyra's and Lion-O's display of loyalty to each other during their match earns the entire crowd's adulation.
In the flashback in "Birth of the Blades", Mumm-Ra displays plenty of this in regards to the Cats and the Lizards. He makes disparaging remarks about the Cats' intelligence right to Leo's face and treats the Lizards as cannon fodder.
A Fete Worse Than Death: The Angry Mob of Thunderian townspeople thinks it'd be fun to cap off Grune's homecoming festival with a bit of Lizard lynching. Lion-O and the Lizards aren't so keen on the idea.
Fighting the Lancer: The frequent manifestation of Lion-O's Sibling Rivalry with Tygra. Feeling testy over Tygra's petty insults, Lion-O challenges him to a match of Thundera's Chase FightGladiator Games, hoping to embarrass him in front of Grune. Lion-O is defeated soundly, and publicly humiliated. Otherwise, they tend to engage in back-and-forth sniping, like arguing over whether to retreat from the Lizard army.
Final Exam Boss: Lion-O uses the lessons he learned in his Trials to save the Cats in the 16th episode.
Other characters get this too, seeing as how the main cast is (basically) barefoot.
For Doom the Bell Tolls: When Tygra beats Lion-O to the bell in their racing game, Lion-O hears the ominous sound of his reputation taking a further hit, along with his brother's gloating and the crowd's cheers.
Forgetful Jones: A species-wide attribute of the Elephants, all very forgetful and absent-minded.
Forgiveness: Allows Tygra to release his biological clan from a curse of undeath.
"Friend or Idol?" Decision: In "Birth of the Blades", Mumm-Ra forces Lion-O to choose between Pumyra and the Sword of Plundaar. Lion-O chooses Pumyra, shifting the balance of the war in Mumm-Ra's favor but also proving to Pumyra that he is a king worth following.
Fur Is Skin: Played with. Though all Thundercats have Facial Markings, all save Tigers have significantly different coloring for their "skin" than they do for their "hair," particularly in the case of Panthro's blue-grey Furry Baldness as offset by his jet-black muttonchops.
Furry Reminder: Real animal growls, whines and hisses are used to punctuate when the Animals of Third Earth are feeling emotionally agitated.
Future Imperfect: Cheetara relates an oral history of the supposed creation of the Book of Omens. It is remarkably off-base, suggesting that even members of the Ancient Tradition like herself don't know the whole story.
Wilykit: Ooh, I know what they were doing! [makes kissing noises]
Lion-O: NO. We were... just... trying to get my sword to work...
In Episode 14 "New Alliances," we get this little gem:
Cheetara: That reminds me: thanks for watching my back. [kiss]
Tygra: Well, your... back's real easy to watch.
Please note, this was the first episode to air in the new time slot traditionally reserved for younger demographics.
Also provides an in-universe example of the trope, as the Thunder-Kittens are standing right there during the exchange, and completely miss the innuendo. As a pair of 8-year-olds, they react accordingly. Especially Wilykat.
In Episode 20, "Curse of Ratilla", Tygra and Cheetara are caught in a cave-in. Convinced they're going to die, they kiss. In the next scene, the cave-in stops.
Glad You Thought of It: Jaga pulls one of these, carefully cloaking references to "Sight Beyond Sight" in aphorisms about kingly behavior, to coax Lion-O into admitting he's had a vision. Unfortunately, he decides that having won Lion-O's trust, the details can wait...
Grave Robbing: The Thundercats perform a heroic variant, since the Book of Omens is kept in the Tower of Omens, which served as the final resting place for the Clerics who transported it there.
Great Big Book of Everything: The legendary Book of Omens, both an ancient history of Thundera and a Tome of Prophecy and Fate, assumed lost. Generals Panthro and Grune mounted a futile search, but during The Siege of Thundera, Jaga informs Lion-O that it exists, and sends him racing to find it before Mumm-Ra does.
Great Offscreen War: Beyond the conflict with the Lizards, the inferred historical conflicts that "brought law and order to a world of warring animals."
Green Aesop: "The Forest of Magi Oar" has "There's no justification for disrupting ecology with rampant industrialization."
Jaga's Opening Monologue neglects to mention that Third Earth's "peace and prosperity" belongs to the upperclass Cats, or that the ruler's "just heart" does not extend to other species.
Grune pulls a doozy in his Death Notification, particularly when he notes "It is only through [Panthro's] sacrifice I stand before you today."
Hammy Herald: In disguise, Mumm-Ra manages to pull off being his own herald as a method of showing off, smugly adopting a telltale Voice of the Legion and boasting of the existence of "the things of your worst nightmares" before dropping his facade and making his Big Entrance.
Hands-On Approach: Cheetara holds Lion-O's shoulders and tells him to relax while advising him on how to induce Sight Beyond Sight. Lion-O does not relax.
He Didn't Make It: Grune performs the silent headshake variant when telling Claudus of Panthro's loss
He Who Fights Monsters: Lion-O discusses this trope in regards to the Cats' war with the Lizards while explaining his defense of the Lizard prisoners and demanding their release.
Hearing Voices: General Grune hears the evil variety, courtesy of Mumm-Ra.
Kaynar also apparently hears voices in his head because he's insane. He also likes talking back.
The Hedge of Thorns: The Briar Woods serves as one to the Thundercats, who enter to flee their Lizard pursuers, get lost, and search for a way out along with the Lilliputian Petalars.
Here We Go Again: In the two-minute short "Snarf: Butterfly Blues" Snarf goes to enormous lengths, risking his own hide to keep baby Lion-O from harm while he chases butterflies. Snarf finally puts Lion-O to bed, only for him to awaken at the sight of even more butterflies!
In "Omens Part 1" Lion-O's "tell" when lying about whether he's seen anything in the Sword of Omens, which Jaga can see right through.
In "Legacy" it's Leo's "tell" when his superior makes noise about a rebellion, though he doesn't catch it.
Hey, Catch!: During Lion-O's Rite of Passage, Tygra abruptly yells this while tossing Lion-O a practice sword, giving Claudus an opening to charge at Lion-O with Sword of Omens in hand.
Hidden Elf Village: The Tiger clan has spent generations in a secluded village in the mountains after their ancestors were shunned by the other Cat clans because they remained loyal to Mumm-Ra during the rebellion. The Tigers' pride and reclusiveness ultimately dooms them.
Hidden Purpose Test: Lion-O's Rite of Passage is not just a test of his skill at handling the Sword of Omens, or the Eye of Thundera deciding his worth, but specifically whether he's able to see visions within the sword itself.
Hostage for Macguffin: ZigZagged. Grune attempts to engineer a trade: the Sword of Omens in exchange for a hostage he's holding, but Claudus rejects the offer, and both the Clerics and Lion-O interrupt Grune's retaliation long enough for Claudus to mount a successful rescue. But the hostage isn't Panthro...and isn't a hostage.
I Am Your Opponent/I Got You Covered: Tygra jumps in when Lion-O puts himself between two stockaded Lizards and an Angry Mob that wants to make him move, informing the crowd "You better be sure you want to do this because I've got his back." Cheetara soon follows suit.
I Have This Friend: Inverted, when Jaga gently nudges Lion-O towards admitting that he's seen a vision in the Sword of Omens by announcing that "The Book says that our greatest king will possess the ability of "Sight Beyond Sight," which has the desired effect of prompting Lion-O to ask a Trial Balloon Question... "Like having visions?"
In "Omens Part 1" Tygra goads Lion-O into a telegraphed move during their Chase Fight game with a calculated: "When it comes to everything except the crown, you're always going to be second place." He even lampshades the effectiveness of it: "When are you gonna learn, brother?"
In "The Duelist and the Drifter", the Duelist goads Lion-O into a fight by calling him a coward. It works since he also indirectly mocks Lion-O's father Claudus in the process.
Later in the same episode, the Drifter gets in some pointed digs at Lion-O's impatience and overexertion, the better to dance circles around him.
I'm Dying, Please Take My MacGuffin: When the Thundercats flee The Siege, a wounded Jaga insists on stopping to conduct a hasty succession ritual where he presents and fits Lion-O with his father's scabbard-gauntlet, speaks an oath and powers it up by tapping it with his crozier.
Imperial Stormtrooper Marksmanship Academy: The Lizards are pretty bad shots when it comes to dealing with Lion-O and the surviving Thundercats. The Cats themselves almost equally so, the arrows fired against the Lizards hit a grand total of two targets on-screen.
Possibly justified for the Lizards: it's implied that all the hi-tech weaponry they use in the Seige had been locked up with Mumm-Ra for centuries, and they've only just been outfitted with it since Grune opened the sarcophagus. Therefore they've not had a lot of time to practice with it.
Impossible Task: A sullen and paranoid Grune discusses his and Panthro's thus-far futile search for the Book of Omens this way, rapidly escalating into declaring it a Snipe Hunt and a Uriah Gambit engineered by Claudus purely to get him out of the Kingdom. Panthro can only snap incredulously at him, and wonder why Grune is ranting about Claudus fearing his ambition.
Inexplicably Tailless: In-story, there has thus far been no explanation as to why lowerclass Cats like the Thunderkittens have tails, while the upperclass do not. However, it's All There in the Manual that tails are the distinguishing marker of Thundera's Fantastic Caste System. In particular, Panthro has an obvious tail in flashbacks but none in the present.
In a brief flashback in "Between Brothers", we see a younger Panthro, without the muttonchops and scars; he looks just like his classic incarnation.
Internal Reveal: When they're Locked in the Dungeon, Lion-O admits to Tygra that he saw a vision of Mumm-Ra in the Sword of Omens just the day before. Tygra does not take this well.
Ironic Echo: The defeat of your enemy is worth any sacrifice.
"You like her, don't you?" Both times spoken to Lion-O about two very different women. The first time he denies it, but the second...
Irony: Between Lion-O and Tygra, each brother wants what the other has. Tygra wants the throne and can never have it, Lion-O really doesn't want to be king all that badly but was chosen for it, all he wants is to beat his brother at something and never can.
In "Recipe for Disaster" Cheetara comments that Pumyra "isn't exactly the friendliest cat" only for it to be immediately followed by a scene of her tenderly helping a baby creature back to its nest.
It Got Worse: In the two minute short, "Snarf: Butterfly Blues," Snarf's life gets difficult the very second after an infant Lion-O sees a butterfly.