Downer Ending: Cartman ends up killing Polly Prissypants after it turns out he killed his dolls through her while Stan, Kyle, Token and Kenny look on in horror and the 99% rally fails to achieve anything beyond devolving into class warfare.
Dude, Not Funny!: Invoked in-universe. Stan and Kyle confront the Fifth Graders about what's been happening to Cartman because they think they're the ones who are messing with his stuff. Stan understands that they're pissed at Cartman, but felt that the fire in his bedroom was taking it too far because Cartman might have actually died. Of course it turns out it wasn't them but Cartman himself who was destroying his toys.
Growing Up Sucks: After being made fun of for playing with dolls and being told to grow up, Cartman "kills" his toys.
Insane Troll Logic: Cartman is so messed up that the only way his brain could conceive the idea of getting rid of his toys is by viciously mutilating them and pretending that someone else is "murdering" them, which turns out to be one of them he then repeatedly shoots as a Mercy Kill.
I Reject Your Reality: It's entirely possible Cartman actually thought his toys were real people and that he wasn't just pretending someone else was destroying them.
Killed Off for Real: Clyde Frog, Peter Panda, Muscleman Marc, Rumpertumskin and Polly Prissypants
Never My Fault: All the kids in school are understandably pissed off at Cartman because his poor health brought the entire school average down so they have to take extra P.E. classes, but he thinks they're just mad at him because they don't want to be mad at President Obama.
Shoot the Dog: Cartman shoots Polly Prissypants in "her" request.
Cartman finding Muscleman Marc boiling in a pot resembles the "bunny boiler" scene from Fatal Attraction.
The entirety of the murder plot concerning Cartman's toys seems, surprisingly enough, based off Umineko no Naku Koro ni.
Take That: South Park proceeds to tear up both sides of the 99%/1% rally. Making the 1% personified as one who deserves it (Cartman) and making the 99% Well meaning but poorly executed protesters that forgot what they were protesting about.
Understatement: Liane Cartman tells Token's parents, after they watch Cartman argue with and then shoot his Polly Prissypants doll, that he tends to be "A little dramatic." Not even she believes what she just said.