mindshade

a person who will mention obscure and scary knowledge during a conversation to the extent that after being around them for a while some of the things the mindshade says will begin to fester in your head and cause you to come back to them for an explanation as to what the mindshade said.
a mindshade is known to cause temporary insanity in those around him/her, the mindshade uses this to get his/her way with ppl