This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Boards of Canada
The entirety of Geogaddi is deeply unsettling, with deceptively sunny keyboads filtered through tape recorders that make them sound broken and distorted. Particularly creepy tracks include:
Right out of the box with "Ready Let's Go", which is little more than an oscillating drone.
"Music is Math," the second track and the first full song on the album, sets the tone. The lyrics are hard to make out (as they're being sung in a near-incomprehensible, tribal wail filtered through a vocoder) but consensus seems to be that they are: "we all fall down... we all fall down... down..."
"You Could Feel The Sky."
"1969" crosses Boards of Canada's Right to Children-era sunny sound with unsettling vocoder bits and references to cults. In fact, it's about the Branch Davidian cult, which maintained a Stepford Smiler facade while their leader sexually abused children.
"A is to B as B is to C" , with its strange, garbled loops and samples. Towards the end of the track, an ominous backmasked chorus chants something that sounds astonishingly like "O Geogaddi! O Geogaddi!"
"The Devil is in the Details," which is about hypnosis. Not a good idea to listen to in a dark room.