In Episode 11, Sullivan browses some artwork of the characters and is very impressed by what he finds...until he comes to a ponified drawing of himself, a Rule 34 picture of Winifred in BDSM, and Wexle as a stereotypical anime schoolgirl. It's even funnier when you know that all those pictures are actual fanart.
Sullivan: Lucy, have you got a fuckin' DeviantArt?
Episode 20
Lucy criticizes artists who attempt to merely replicate reality instead of drawing something original, mocking Shuck by telling him to "use his imagination" when drawing her portrait. He responds by drawing her in an extremely sexualized pose, basically a "Draw me like one of your French girls"-style pinup poster, with her speech bubble in the drawing reading "USE YOUR IMAGINATION DADDY".
Sullivan (with Shuck's help) apparently killed fifteen people just because they had pumpkins he wanted.
Sullivan:(showing off his pumpkin carving) Dahh!! [nobody reacts]...Well don't all clap at once.
Fleischer: So. How many people did you kill for the pumpkin this year?
Sullivan: Fifteen.
Fleischer:Fuckin' fifteen?!
Sullivan: It's not my fault everyone's tootin' bobs! Whenever I try to get something in life, some cunt always tries to take my fuckin' money. And besides, Shuck helped this year.So...
Fleischer: What the fuck do you mean, fifteen?
Shuck: He said I could eat the pumpkins he didn't pick.
Lucy: That's a fair deal!
Fleischer: You are all fucked in the head.
Lucy: The good kind?
Fleischer: There is no good kind!
Bob referring to Yeshua as "red kitty". It's both hilariously wrong and yet so strangely accurate.
Fleischer's utterly gobsmacked reaction when Fontaine and Wexle bring Dorothy's corpse home and chain it to the ceiling.
Fleischer: What the fuck did I miss? What the actual fuck did I miss? Why do I leave you alone for FIVE MIN- (Smash Cut to credits)
A subtle visual gag in "Don't Panic": While most of the others are leaning against the door frame or placing their arms on the table surface, Ludwig is so tall that he can casually rest his elbow on top of Sullivan's refrigerator.
The 2017 Halloween video, where it's revealed that Sullivan didn't just murder an entire family just to steal a pumpkin from their pumpkin patch, he beat them to death with the pumpkin, then he stole it. Fleischer's understandable dismay makes it all the more hilarious.
The 2019 Halloween video which features Sullivan and Xander (one of the few other humans on the show) teaming up to murder a random lady and steal a pumpkin from her.
Sullivan introduces Xander to Lucy only to learn they've met before. Lucy comments that she likes him and won't kill him....yet.
. There are no words.