Grim: I don't know! (grabs Billy and hugs him) But I'm gonna hold ya tight and never let go!
Billy: I love you, Grim!
Irwin: What about me, yo?!
Grim: Eh, you'll be fine.
Then there's the scene where Mindy snaps her fingers at Mandy in defiance, as if she's channeling Sassy Black Woman.
Mindy: Last year I was Little Miss Rickets, the year before I was Little Miss Toejam, and girl I'm gonna be Little Miss Scurvy!
This rather hilarious exchange:
Principle Goodvibes: But before we begin, let's take a moment to think about why we're all here...
Man in audience: My wife made me come!
"Wishbones", where a Jackass Genie skull is granting characters' wishes. When Pud'n picks it up, he wished for "a cute little bunny that will love him". The result is a cute, pink rabbit who speaks in a demonic voice and, well...
Boogey: Is it not true that not only was your scythe stolen by a headless man wearing a pumpkin on his neck, but was also taken by Billy, Mandy, Irwin, Billy's father, Billy's mother, Billy's cousin (Nergal Jr.), Billy's cat, Dracula, General Skarr, Principal Goodvibes, Mrs. Claus, the Secret Snake Club, the Army, Scout Troop 701, the Sleestaks, the President, the mailman, the Dingleschmidt sisters, the Boogeyman, a llama, and a turkey salad sandwich... (ominously) hold the mayo?
Also from the trial:
Boogey: "I'd like to call to the stand my first witness (summons a flaming chair out of the lava, which gets sprayed with a fire extinguisher)... myself. (Sits down in chair and removes glasses) Hello, I'm the Boogeyman!"
The bit with Grim chasing Skarr, but the best line has to be:
Grim: You can't outrun Death!
Skarr: That's why I have turbo!
Shortly after the above moment:
Skarr: Hey, what does this do? (pushes a button. It fires a laser which burns through his shirt and reveals the hole in his chest)Oh, yeah.Now I remember.
After the gang come home having failed to catch Skarr, Harold points out that he gets fired from all of his jobs and got fired from his most recent one after eating all of the paper cups. Gladys overhears this and threatens to stab him with a heated pike.
Billy's musical number, Scary-O.
After Irwin single-handedly rescues Mandy from Boogey with the Power of Love and breaks the nightmare spell by kissing her, her immediate reaction is that she's still in the nightmare. Irwin then tells her otherwise, causing her to retch over the side of the boat.
The part where we find out that Numbuh 3 is the replacement Grim Reaper.
The Hole of Oddities, where they turn into hand puppets:
Billy: AAAHHH! I'm a forearm from the waist down! Billy, Irwin, Mandy, and Grim: AAAAAHHHHHH!
The fact that they play this exact same flashback three times.
Or the part when Billy enters the dwarf's flashback, shocking everyone in said flashback.
At the beginning Billy has made a huge mess in the kitchen to make one sandwich, one of the ingredients being a pink turtle, which is still alive.
Billy meeting and running away from a disheveled Yogi Bear. The best part is either when Boo-Boo comes out of the bushes revealing that he's now absolutely huge or when Yogi says he knows Billy is close and calls him dirty, to which Billy points out his last bath was over two weeks ago.
The part where the dwarves catapult Billy, who is disguised as an elf, into the elves' factory and he flies over Grim and Mandy:
Grim: (helping Mandy wash a car) I wonder how Billy's picnic is going.
Billy: (flying overhead at high speed) HEY GRIM HEY MANDY!
Grim: That answers one question, yet raises so many others.
(Mandy sprays him in the face with the hose)
The line "And here is the dwarven closet of cleaning supplies!"
A Drill Sergeant Nasty voiced by theR. Lee Ermey popping up to say that the battle scene would be too gruesome for the target audience, and then rambling a bit while Relax-o-Vision of a koala played. He cuts it back to the action too soon, then told an anecdote about a guy who "misread the signals."
The aforementioned turtle also appears in "5 O' Clock Shadows", where the trio first arrive in the shadow world while Billy laments that everything looks the same.
Billy: Same! Same stupid rug, same stupid couch, same stupid turtle... (turtle slowly walks over) Hey! A turtle! (the turtle bites him on the nose)
Mandy: Same stupid Billy. (smacks Billy, which causes the turtle to go flying across the room)
Billy and Mandy's counterparts in the shadow world. Shadow!Mandy is sweet and obsessed with unicorns, much to Mandy's disgust. Shadow!Billy is even dumber than the real Billy and his only means of communication are barking like a seal.
The entirety of "Everything Breaks" can probably qualify. It features highlights such as Billy smashing through the floor of his bedroom and landing at the kitchen table, throwing his bowl of cereal out the window after complaining that it's not pancakes (after which the bowl violently explodes), hijacking a school bus and driving through Skarr's garden on the way, and flooding the entire school— and that's just the first few minutes!
Lord Pain "punishing" Billy... by going around breaking everything with him. And earlier, when they break Grim to pieces and his bones scatter across the screen.
Lord Pain showing Billy what his antics have wrought on his neighbors, with Harold trying to defend against an angry mob in a Frankenstein-style setting. He throws Gladys at them, to which she tells them he always gets that way during football season.
The episode when Boogie first appears and Billy and Irwin are watching TV:
Irwin: This show is awesome.
Woman: Hey Doc, what are you doing with my legs?! (razor sounds) AAAAAAAAUUUUUUUUGGGGGGGGHHHHHHHH!!!!!
Doc: Oh stop it, I'm just shaving you.
Billy: Oh, Grim? The TV wants to talk to you.
Boogey: ''(Still diguised as the TV, holding a wine glass) Hello, Grim.
Grim: (Perplexed) ...Hello, TV.
"REWIND! FAST-FORWARD! REWIND! FAST-FORWARD!"
At the beginning of "Prank Call of Cthulhu", when Grim provides one of his ominous warnings to deter Billy from using the Phone of Cthulhu, Billy points out that his eyes are still on fire after he's done. He asks for something to put the fire out, and Billy gives him a pitcher of coffee, a bottle of hot sauce, a barrel of acid, and a container of rocket fuel, the last of which sets most of his head on fire and he runs to the bathroom (which Harold was in) to put it out.
The monster who communicates by beatboxing also deserves mention.
In "Nergal's Pizza" Irwin, who is working at Grim's pizza restaraunt that's at war with Nergal's, annoys Nergal over the phone so Billy can pour dirty laundry into his sauce pot like Grim claims he uses in their commercial (after Nergal said Grim makes his pizza with bugs). Cue Nergal's ClusterAngrish Bomb when he sees the sabotaged pot.
Later on the second time Nergal Jr. infiltrates Grim's place he gets caught, and then sent back to Nergal in a pizza box. When Nergal opens the box Jr. complains that the pizza he was on had anchovies.
The very beginning to that episode, when, with no warning, Nergal breaks through the surface of the earth, carrying a pizza, in the middle of a busy intersection, causing a few cars to fall into the chasm. He then proceeds to yell apologies back at the cars. Gets this editor every time, even when I know it's coming!
"Dream Mutt" had its moments, but the funniest is when Billy's new dog, Wiggy Jiggy Jed, wants to sleep in his bed, and Billy flails his arms at him in a ludicrous fashion:
Billy:(flails his arms with each sentence)NO!! Bad dog! This is my bed!
Jed being essentially a pastiche of the snarky, fourth wall breaking Hanna-Barbera characters of the 60's and 70s. Also, his evil plan of world conquest, which turns out to just revolve around taking every bed in the world.
Billy telling Jed to turn off his annoying walk theme song, since it's late and people are trying to sleep.
This exchange from "Guess What's Coming To Dinner?", in which Hoss and Eris are posing as Billy's parents:
Eris:(indicates Hoss) This is Billy's dad, (indicates herself) I'm Billy's mom, (pulls out a trout) and this is a trout. (she proceeds to smack Goodvibes around the head with it)
Principal Goodvibes: ...Why did you just hit me with a trout?
Eris: Because the mackerel wasn't fresh.
Another moment from the same episode:
Mandy: Rollington Academy is for...
Billy: Geniuses! Which I is one of am!
Billy: Ask me a question. Give me a challenge. Anything at all.
Earlier on Harold suggests that Billy build robot duplicates of himself and Gladys. Billy points out that he already did; cue flashback to giant robots of his parents Gone Horribly Wrong.
Harold: ...oh yeah. Man, I'm still paying off that bill.
Delgado and Eris constantly mispronouncing Goodvibes name. In the end he finally just gives up on correcting them.
Billy does get admitted to the Rollington Academy thanks to Goodvibes giving him a recomendation after Hoss threatens to beat him up. His original suggestion was that if Billy worked hard and focused on his studies, he could have a bright future as a speed bump. The real clincher? It turns out that Rollington is a military academy.
Hoss Delgado calling Mandy a "fishwoman", and her reaction to it.
From "The Loser from the Earth's Core":
Nergal: And so you see, Billy, I'm a sad, sad failure. I can't ever show my face in that household again.
The scene where Grim accidentally drives himself and Dracula into a ditch. As they're walking in the hot sun, they get picked up by a truck driver whom Dracula gets mad at. As they play "the game" (Connect Four) to calm the driver down, Grim asks Who Is Driving?. The truck lands in the very same ditch.
Grim:OH GIVE ME A BREAK!!!
Also, the creepy trucker, who even freaked Dracula out with his hobby of making sunglasses from discarded nails, thinks THEY are too weird, and decide to set off on his own after the crash.
Any time Billy's face gets blown or ripped off:
The beginning of "Tricycle of Terror" has him crash his bike into a tree and he flies off, grinding his face across the road and looking up at two girls working a lemonade stand, his face now ripped clean open much to their horror.
In "Reap Walking" when he's making waffles (despite the fact that he obviously has no idea how to), he puts his mouth on the egg beater while it's still on, which then rips off his face. He says the batter tastes smooth.
In "The Loser from the Earth's Core" when Nergal pulls out an analog lawn mover that he borrowed he throws it away and it lands on Billy's face tearing it clean off.
In "Billy & Mandy's Big Boogey Adventure" when Future!Billy (from the post apocalyptic Endsville ruled by Mandy and later by Fred Fredburger after he alters the timeline) goes back to the future he blows Present!Billy's face off, after which Present!Billy states "I like that guy".
During Grim's first story in "Short Tall Tales" Billy (as Pecos Bill) gets his face ripped off while battling the tornado.
The scene where Pud'n runs in fear after seeing the skull from a biology skeleton in the toilet (Billy replaced the skeleton with Grim in an effort to cheat his way through a test, a plan which backfired horribly since it was a math test and he told Grim it was history, which is Grim's best subject). He runs straight into a janitor and they both tumble down the stairs. Later on when he sees Nergal Jr. wrapping Ms. Butterbean in his tentacles, he runs into the janitor AGAIN (who now has a cast and bandages) despite the latter's obvious attempts to get away. Then they fall out the window... from the top floor...which gradually pans out and reveals the school is located on a tall mesa overlooking a desert.
When Billy replaces the biology skeleton with Grim he comments "Billy, you said we were going to the morgue."
Billy's reaction to Grim saying he's not good at math: "What's math?"
Later on after Jr. has taken on Ms. Butterbean's form he reveals that Billy drew a doodle of a clown with a flamethrower in place of an actual answer. Billy tries to remedy it by giving it a pirate hat.
When Billy and Sperg are in detention Mandy is still there simply because she wanted to watch Sperg get his comeuppance. She shows him her test paper has an A with 6 pluses.
At the end Pud'n looks in the toilet again and sees the skull is gone, but then looks up and sees Ms. Butterbean stuck to the ceiling with packing tape. It's only after he sees Grim that he faints.
In "Irwin Gets a Clue" there's a scene where Hoss and Irwin are in the former's truck and since's he not paying attention to the road at all he ends up driving into Snagglepuss, Yogi, Boo-Boo, and Huckleberry Hound. All of them except for the first one get caught on the windshield before flying off.
The beginning of "Detention X" where Billy assumes he killed Ms. Butterbean with a rancid apple (he didn't). His exaggerated reaction is what seals it:
Billy: My legs! (cringing) My lungs. Mandy: Face it, dweeb, you're out of shape. Billy: It isn't true! Mandy: Whatever. See you at school.
When Billy and Jr's plan to pass the fitness test goes awry:
Grim: Billy's out of control! Somebody do (realizing that Mandy's lack of enthusiasm sums up how both of them should feel) ...some...thing. (to Mandy) You're right. He's gone. Let's go sell his things.
The montage from "Lil' Porkchop" with Billy tending to Porkchop. Naturally Billy doesn't realize he needs water and keeps exposing him to heat, starting by taking him to a playground (on what he says is the hottest day in the history of the world) and putting him in the sandbox, then taking him to a tanning booth which burns him to a golden brown, and finally taking him to a restaurant where after eating the food he yells in pain and falls through the wall, after which he crumbles.
(Beat, all the doctors run out of the room, screaming)
In the episode where Billy is replaced, there's one scene where the rooster belches as the sun comes up. Made funnier by the fact that chickens are incapable of that function.
In "Ecto Cooler" when Billy consults his father on having a spectral arm (which belongs to the ghost of Lord Byron) in his throat, he freaks out upon seeing it, then becomes an emotional wreck frantically asking how that could have happened to his son. Made more hilarious by the fact it's ridiculously out of character for him.
In the same episode Billy assumes that Sperg's weakness is his mom after analyzing the old-fashioned MOM heart tattoo on his arm. He writes an "ode" to her, which in actually is just a bunch of slander culminating in her being so ugly staring at will cause your head to melt. Sperg's mom then actually shows up, crushed by Billy's words, and is actually quite attractive, but when Principal Goodvibes looks at her the flesh on his head actually melts off.
The Gainax Ending of "Billy Gets an A": Grim and Mandy go back in time to prevent Grim from changing Billy's test score to an A. Their first attempt fails when present Grim distracts past Grim and Billy takes the latter's scythe and changes his grade himself. The two Grims go back further to convince Billy to study and he does but still fails. With three Grims in tow they fail going back to stop Billy from being born, then they fail going back to stop Billy's Japanese ancestor from being married, then further and further until eventually there's a whole bunch of Grims at the dawn of time who run away simply because a dinosaur with Harold's coif burps. Present Grim asks how all of it will end... then it cuts to a "The End!" card.
Billy's breakdancing in "Terror of the Black Knight".
In "Hoss Delgado: Spectral Exterminator," the singing dinosaurs and Hoss's reaction to them:
"He's raising an unholy army of singing dinosaurs."
In one of General Skarr's episodes, Grim and Mandy are in their living room discussing how Skarr always gives them a creepy look, and then Grim says he's doing it right now. We then see that Skarr's face pressed right up against their window with a deranged grin on his face. It's the comic timing that really makes this scene work.
In the same episode, Billy and Grim are playing football in the yard, and Billy is frantically shouting "Grim! Over here! I'm open! GRIIIIIIM!". Grim is standing about two feet away from him.
In "Mandy Bites Dog", Mindy gives Saliva a harsh Reason You Suck Speech after he licks her, but then Saliva snaps and scares the crap out of Mindy. As she flees, he tries to imitate Cerberus leaping through the air, but falls on his back.
Mandy: (facepalm) Nobody saw that, right?
The first time hearing Dracula speak, and realizing that it's friggin' Blacula.
"Corny!? You callin' Dracula corny!? *CHOMP*"
From "Toys Will Be Toys:"
Billy: ''*in tears* Oh, Grim, why do the good die young? Grim: Well, usually because I get confused.
When the Jurassic Creeps try to get by Grim by hiding behind an unconscious Milkshakes that they previously shot with a laser:
Grim: Milkshakes, where are you going? Triceratron: To destroy all that is good. I mean, meow.
Billy's Humiliation Conga montage in "Dumb Luck", particularly when he ends up pouring a lump of expired milk on his cereal then gives it to Milkshakes, who licks the milk and becomes stunned.
In "Test of Time", when Billy and Mandy use Grim's universal remote to go to the future, they see that it's apparently taken Billy 42 years to write a report.
The ending: Billy, Mandy, and Old!Billy end up causing a Time Crash and Billy gets sent back to the stone age, where he falls in love with a cavewoman. Cut to millions of years later where Billy is the genetic ancestor of all human life on Earth, and everyone has his eyes, nose and intellect. And due to Rule of Funny, the change has apparently affected animals as well.