Various closeups of disturbing, unnatural and violent images and loud sounds.
The Reversed and distorted music can make the series have more of a terrifying theme to it
The robots do look pretty terrifyin'
The robots move (dance almost) in unnatural and frightening ways.
It says it right at the genre of the series (which is ARG, aka Alternate Reality Game). If you do not know what ARG's are, it is a series that you need to solve the plot and lore by yourself. ARG's are usually scary, but some aren't. If you really want to see this, beware from loud jumpscares, disturbing imagery, frightening secrets and of course, bodies being stuffed into animatronics.
If this series were to be rated by the MPA it would be rated R for strong disturbing violent content throughout, including bloody images, substance use and references and some language.