Where do you start?! I've read spooky pokedex entries that make Cubone's entry look like a Mickey Mouse Christmas celebration.
The one that scares the willies out of me is Parasect. I had barely noticed this Pokemon until I read a certain creepy pasta. I did some research, hoping that this was just a story ... its not. Parasect is a walking corpse. Its dex entries have all been pretty clear about this from the time that this pokemon was introduced in gen 1 till today.
Its Ultra Sun entry entry has not changed, "The bug is mostly dead, with the mushroom on its back having become the main body. If the mushroom comes off, the bug stops moving."
Parasect eyes don't have any pupils anymore like they did as Paras. What I thought were just a pair of big, stylized cartoon eyes really scare me now because I understand that Parasect's eyes are meant to show that you are staring at a vegetable without any conscious or soul. Parasect can't think.
Its not just the idea that you are playing with a zombie that is creepy, but that evolution is what signals this pokemon's death. When it evolves it is being taken over and killed by the deadly parasitic mushrooms sprouting out of its body. Its creepy, and it's sad. If you raise Paras to Parasect then you watch your pokemon die in front of you, worse you killed your own pokemon!
This makes the episode the Problem with Paras really bother my conscious now.