This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Bee and Puppycat
Wallace's transformation/possession, where the monster woman pours out of his mouth. His eyes turn wide and red, sharp teeth appear in his mouth, and then the fact that her appearance is accompanied by gross, wet sounds.
The monster herself, with two large, fanged mouths that cover her face, her vein covered grotesque body, and five sharp spines coming off her back.
The cherry that can steal fricking souls. Period.
The farmer himself when he reveals that Bee is the fertilizer. The dark shadows cast over his face when he says it don't help.
Toward the end of the episode, the Farmer gets swallowed alive by one of his animals, which in turn gets eaten by another animal...which then gets eaten by another one...
What was the intended payment for the job? "The sweet release of death."
Keith is annoying the protagonists with his obsession with cleavage. Puppycat's response when Keith asks for ice cream cleavage is really jarring.
Bee's new friend gets pulled into a black hole and she tries to pull him back out, result in her arms getting sucked in. Something cracks, ribbons flutter out of the black hole and Bee's arm is revealed to be robotic, with shattered circuitry and big sections of skin peeled back, and ribbons spilling out of it. The dream in Food where ribbons spill out of her gouged wrist suddenly makes a lot more sense.