Angst? What Angst?: Beeza and her species in "The Ball" had to constantly move from planet to planet to escape from Buster, who practically destroys not only the planet but all the hard work they had done in it. Sure, they treat it as routine, but it gets worse when she mentions that they have no planets left and they will just keep flying until they run out of fuel or food, whichever comes first.
Awesome Ego: Lord Hater definitely, but to a lesser extent, Emperor Awesome fits this by trope and even more so by trope name.
Base Breaker: Wander, the lead protagonist, has become this. Many fans love him and find his antics entertaining and fun, but others find him incredibly annoying and uninteresting compared to Lord Hater.
Bizarro Episode: "The Void", in which Wander and Sylvia visit a white space (think Michael Crichton's Sphere) where anything either of them dream up comes immediately true, and the rules of logic and common sense do not apply. It's pretty much non-stop insanity from start to finish.
The plot of The Battle Royale has stirred up the fanbase. Some have vocally expressed disgust of Wander trying to fix Hater up with Dominator after discovering her secret since it feels that Wander is using her as a tool to make Hater good. Others have looked over this problem and have faith that Dominator will still be her own person, and vicious threat to the galaxy, and it will lead up to Wander's own character development.
The ending to the episode, too: Some are excited to see what will happen now that Hater has a crush on Dominator, other's are calling it a cop out and are worried the romance will take over the show. It later turns out that the latter is not the case.
Crazy Awesome: Wander, continually saving planets by basically acting like a complete goofball. Highlights include stopping a feud in "The Good Deed" by acting out an elaborate courtroom scene by himself and literally confusing everyone into submission, to saving an entire planet by wining a dance off in "The Party Animal".
In "The Boy Wander", Dr. Screwball Jones gets this with his tickle machine. Subjecting Tickle Torture on unwilling subjects, and then overpowering Hero!Wander in a fight? Deliberate Nightmare Fuel and suspense. Doing it while singing a polka Villain Song? Hilarious.
In "The Black Cube" when everyone where confessing their bad days, one of the gang of teenagers mentioned that he is suffering from a distinct case of ennui... but then he admitted that he use words he doesn't understand to sound important.
Lord Dominator slowly petrifying Emperor Awesome with cooled lava as he looks on in complete and utter fear is actually kind of horrifying. But then...
Awesome(afraid): Don't be like that babe! Come on, what about the good times? Hey... take it easy D!
Lord Dominator: That's Lord Dominator if you're nasty.
Peepers too. Although he is The Dragon and quite ruthless, he also earns sympathy for being a cute little eyeball that is good at his job and would have conquered the galaxy earlier if not for Hater's terrible leadership. He also spoke for so-called "nerds" everywhere in his Hannibal Lecture to Emperor Awesome.
Lord Dominator is getting a lot of this based on the previews alone. The reveal that she's actually a Green-Skinned Space Babe under all that junk probably helps a lot. In fact, her Villain Song in "My Fair Hatey" can be seen as a Take That towards this trope.
The Tumblr fandom was excited for Westley months before his episode aired. When the episode finally came out, the fans were not disappointed.
Heck, all of the Watchdogs could count as this since they get so much love and attention from the fandom.
Some background characters are popular in the fandom because of their design. Most notably, the pink and green alien who appears at around 0:19 in the theme song has quite a bit of fan-art for a character who has never appeared in the show.
When an airdate for "The Enemies" was announced, Brad Starlight got a small fan-following as well.
Lord Dominator, and how!
Dr Screwball Jones. Being voiced by Weird Al certainly helps.
The Revealthat Lord Dominator is actually an Adorkable girl not unlike Wander in terms of personality has resulted in many people shipping Wander/Lord Dominator or even Hater/Dominator
After the summary for The Battle Royale came out, Hater/Dominator spiked in popularity. It helps that Wander ships it in canon.
Heck, the fandom pretty much ships almost every character with every other character. Wander/Peepers, Peepers/Sylvia, Sylvia/Dominator, you name it. See Idiosyncratic Ship Naming for more.
Fanon: Wander is often called a "star nomad". McCracken did call Wander "nomadic" and there's a star on his hat. This also became in-universe Fanon in "The Legend" when a girl talks about her fanfic of his origins.
An odd inversion. In "Battle Royale" Wander defeats Dr. Screwball with a "Bang!" Flag Gun, prompting the latter to enact an overly dramatic death scene. Hilarious? Yes, only it recalls when the DCAU Joker died due to a Brainwashed and Crazy Robin shooting him with a lethal version of the gun. Bonus points for Wander being in his "grim and gritty" heroic mode.
Emperor Awesome hitting on Sylvia, especially Sylvia's reaction. Then Awesome tries the same on Dominator and gets coated in lava, then in the next episode "My Fair Hatey", being trapped in the dungeons, broken.
Harsher in Hindsight: With the news that Disney is pulling the plug on the show prematurely, some of Wander's lyrics from "My Fair Hatey" become extremely painful to long time fans.
Wander: We gave it a go/Put on a heck of a show/And did a lot of fun stuff we'll get to laugh about after...
Heartwarming in Hindsight: The Watchdogs clamoring for Andy's show in "Eye on the Skullship" after Hater forcibly cancels it becomes this in light of the fans doing the same thing on hearing the news that Wander Over Yonder was not renewed for a third season.
While we don't see an owner in "The Ball", Buster does have a dog tag with his name on it. So Beeza and her people have a new home until Buster's owner (or someone else) finds him and decides to give him a bath/flea dip.
Stretching the definition of "inferred", the number of planets that Lord Dominator has destroyed has led to an onslaught of refugees and survivors seeking sanctuary. "The Secret Planet", "The Show Stopper", and "The Legend" actively shows the consequences.
Internet Backdraft: The show being canned after two seasons have enraged people and are going out of their way to convince Disney to resurrect it back, especially considering the reason for the cancellation: The executives felt 80 episodes were enough for the show. This has not gone well for fans.
Lord Hater. He's proven himself to be a very evil and ruthless individual, but he's also a socially awkward Butt Monkey. Certain episodes also imply that he's only evil because he's trying to compensate for his insecurities and really just wants to be popular.
Commander Peepers. Evil bad guy and ruthless second-in-command? Yes. Butt Monkey whose boss is a Man Child and has only recently come to appreciate him? Also yes.
The Black Cube of Darkness may be a soul-stealing Eldritch Abomination, but after the events of "The Black Cube" it is easy to see why he turned out that way. He is staying at a run-down apartment that he can barely afford rent because he has a crappy job at a fast food joint, his girlfriend dumps him, his lack of hands makes even the simplest of tasks a chore, and everyone either hates or fears him because of his power. Even when he saves one of the punks harassing him, a mob forms to attack him. Luckily, things seem to be looking up for him in the end.
A lot of Jack McBrayer's fans took an interest in the show in the first place specifically because he voices Wander.
A lot of fans who don't like Wander or Sylvia but love Lord Hater will only watch the Lord Hater episodes.
Lord Dominator's song "I'm the Bad Guy" went viral on Tumblr (at over 50,000 notes), earning her many new fans who had never watched the show, many of whom only intend on watching the episodes with Dominator in them.
Love to Hate: Fans love Lord Hater, with some even saying that he makes a better protagonist than Wander. Craig McCracken eventually confirmed this was his intent.
Dominator gets this more than almost any other character.
From "The Picnic", Wander carefully scooting down the side of the crater.
Lord Hater is a reaction face gold mine.
Wander taking selfies.
It's quite common on Tumblr for fans to take clips from the show (that involve notable movement) and sync them up to popular songs or pieces of music. Usually the first shot of Wander in the opening, where he's walking with changing backgrounds. This meme even resulted in an official Wander over Yonder promo set to Quest to the Hall of the Mountain King
Photoshopping Lord Hater's face onto gifs of other skeleton characters.
A Freeze-Frame Bonus in "The Waste of Time" gave birth to the (surprisingly convincing) theory that Lord Hater was once an astronaut monkey. This spawned a series of "Lord Hater is a monkey" fanart. Even the creators have caught on to this new meme!
Moe: Wander, all of the Watchdogs, and even Sylvia all have their adorable moments.
In "The Tourist", Trudi crosses it when she pops Wander's bubble and leaves him to die in space.
In "The Bot", we all lose our sympathy for Dominator when she executes Bot 13/Beep Boop after undergoing its Heel–Face Turn. It serves as a reminder that despite her silliness and annoyance with Hater, Dominator is still a serious and threatening villain.
Narm: Prince Cashmere from "The Troll" episode is a tough and brave goat warrior... then he opens his mouth and out comes Patrick Star's voice.
The song "The Commander's Last Command" from "The Axe" contains such silly lyrics as "a sandwich took our planets". Does this make the song any less heartwrenching? Hell no.
The episode "The Black Cube" is about a floating black cube's spiraling depression. The episode has a sense of silliness given the main character but the episode's continuous Humiliation Conga and oppressive atmosphere successfully makes it rather sad.
Private Westley from 'The Little Guy' is extremely popular despite only being in one episode (aside from one cameo in the first season finale.)
Beeza from 'The Ball'
The two-headed fruit bartender from 'The Bad Guy' has a ton of fanart, moreso than any of the other characters in that episode.
The BLACK CUBE from 'The Fancy Party'. It's eerie floating and pseudo-Latin gibberish (as well as the fact that the whole area distorts when it speaks) makes it give off the feeling of being an Eldritch Abomination, making it one of the most memorable of the villains at the party.
The drill sergeant and Giuseppe the Watchdog tailor in "Eye on the Skullship".
Paranoia Fuel: In "The Lonely Planet", we meet a planet who is not only alive, but can control the weather, plant growth, and plate movement, and use those to harm people. How do we know the other planets in this universe (including ours) aren't like this?
Rooting for the Empire: As of "The Cool Guy" and Peepers' Hannibal Lecture to Emperor Awesome about how "nerds" get things done in the world, at least one viewer is rooting for Commander Peepers to spread evil through the galaxy.
They Wasted a Perfectly Good Character: Dr. Screwball Jones. The Evil Counterpart to Wander who is a Well-Intentioned Extremist about spreading happiness throughout the galaxy, and nearly managed to succeed. Come "The Battle Royale," however, he ends up losing to Wander in a Curb-Stomp Battle, then losing off-screen to Lord Dominator before "My Fair Hatey" and doesn't even get to sing again in the latter. Justified as the creators mentioned that they had trouble getting Weird Al in to record more lines for Screwball, as Weird Al was very busy at that time.
Too Good to Last: The show's cancellation was officially announced after the very well received My Fair Hatey.
The opening sequence, showing off the sheer variety to every character and world introduced in the show, repeatedly cycling through different backdrops and aliens- each of which feels different to the last. It's a real testament to the creativity and imagination behind the show.
Wander and Emperor Awesome's dance off in "The Party Animal" has some very fluid animation.
Wander and Screwball's duel in "The Boy Wander" has amazing lighting usage that lends a sinister air to this otherwise silly fight scene.
Hater's and Dominator's fight in "The Battle Royale" is brilliantly animated and action-packed.
Wander at times, especially his helpless persona in "The Wanders" and "The Hole Lotta Nuthing".
Wander's Hat gives the wearer whatever they truly need, but in "The Bad Hatter", it's revealed that the Hat can be tortured into giving the wearer whatever they WANT. It's also revealed that the Hat has had a history of being tortured for its power before Wander came along.