In an episode of The Parking Lot is Full◊, you are informed that you are one of only 23 real people in the world and everyone else is a fake, designed to keep you from the others. Taken to logical conclusions, this becomes even more terrifying. Everyone in your life, everyone you love, hate, talk to, work for, even all the tropers here are designed by some malignant force to keep you from making a genuine connection with one of the few other 'real people'.
For the 2007 Crossover Wars event, a fake comic was created as the birthplace of Villain Henchman Max Catnap, a cat furry with a disturbing hatred of his own kind. The fake comic's progression from crayon-drawn, innocently well-intended furry fare to brutal murder is enhanced by Max's erasing of himself from the archives, revealing the full story only in flashbacks.
The recent Freefall arc in which Florence's short-term memory is impaired as part of an effort to check on her mind, since she's technically an artificial intelligence.
Not to mention that despite being a walking, talking, biological entity, she has a remote control that can turn her off, her brain can be "adjusted" to change her attitudes without her knowing, and every time she interacts with the company that created her, she gives herself a personality test afterward to make sure that she hasn't been "rewritten." If that wasn't enough, when a security guard finds out about it, he yells at one of the developers about it, pointing out that "This stuff could be adapted for humans," and asking whether he should be worried. The developer says of course not: the security personnel are unionized, so the company would test it on independent contractors first.
This strip puts a whole new spin on the Mushroom Kingdom.
In Homestuck, John and Rose (and possibly Dave) all have Rooms Full Of Crazywithout them realising it for most of the plot so far. Apparently, the explanation is that they unconsciously scribble on their walls and then their mind just filters out so they never notice it. Now look around the room that you're sitting in and think about what your subconscious mind has written...
Jade has them too, but she's a subversion; she's consciously aware of them due to writing them in an attempt to motivate John and wake up his sleeping dream self.
Lord English is behind the Fourth Wall. No one is safe.
The Squiddles. They start out as a sickeningly sweet cartoon abut cute silly cephalopods who are running from an evil fisherman and try to fight him with The Power of Friendship and The Power of Love. and then it turns out that this is just what the humans see when they look at them. In reality, they're seeing giant Eldritch Abominations. Now imagine your favorite childhood cartoon for a second. Now imagine that it's actually the human perception of an Eldritch Abomination. Sweet dreams...