Poppy's way of speaking is... approximately how a normal person would speak, but not quite. And half the time, she doesn't look into the camera, but somewhere far away off-screen. As discussed by Titanic, the speech and sound is dubbed over / added in, and sometimes ever so slightly out of sync. This creates an unsettling/fake feel. Titanic Sinclair also does this on his YouTube channel.
This trope even bleeds into the music itself, namely her straight pop tracks after 3:36 (Music to Sleep To). While it still remains as catchy and bright pop, some compositions can get creepily dissonant at times, and her lyrics can occasionally tread into weird territory (leaning on obsessions to technology, strange double entendres or allusions to something more sinister), vague enough to be easily missed, but unnerving once you notice it.
Charlotte. Charlotte is an expressionless mannequin who speaks with a computerized voice. Initially starting as an interviewer for Poppy, Charlotte gradually becomes more envious of Poppy's success so much so, she resorts to using drugs. She also has a son who she tends to neglect.
"Get Away From Me" is another video of something menacing her, and Poppy bemoaning she just wanted to make a video. Comments noted it wasn't directed by Titanic.
Music
"Lowlife" has several disturbing images within it. The most disturbing is where Poppy is sitting down at a dinner table having a conversation with Satan. The "meal" consists of human skulls and other bones.
There's the music video and lyrics to "Time Is Up", in which Poppy essentially gives a "The Reason You Suck" Speech to mankind's folly in ruining Earth with pollution and war, stating in no uncertain terms we'll soon be extinct due our own stupidity but Poppy (whatever she is) will still be here when we're gone, so she's not concerned. Of particular attention is her most blunt verse:
"Meat" from Choke is one of Poppy's most outright morbid songs, detailing the state of humanity after it's been reduced to a farmed food source like cattle. The visceral Sickening Slaughterhouse imagery throughout it is especially disturbing because much of the details of factory-farming animals is real.