Darkrai is the creepiest Pokémon in the entire series, a Pokémon that wouldn't seem out of place as the main monster in a horror movie. If you took Freddy Krueger and made him a Pokémon, he would be Darkrai. Like Freddy Krueger, Darkrai is responsible for causing people to suffer from endless nightmares, to which, in Darkrai's case, they can't wake up from without Cresselia's Lunar Wings, resulting in the deaths of many people in the Pokémon series. This is such a dark fact for a dark Pokémon. The game attempts to rationalize it, perhaps to keep the game rated "E" for "everyone, by mentioning that Darkrai only does it to protect himself from harm. Um . . . my booty that's true! Mr. Darkrai, much more reasonable ways exist to protect yourself, sir! Also, you're a Dark-type, a type that is notorious for using moves that are unethical, so I know you're not above lying to make yourself look somewhat better, Darkrai. Also, anybody that remembers the creepiness of the Darkrai event in Pokémon Platinum involving the dilapidated Harbor Inn in Canalave City and Newmoon Island would likely agree that Darkrai wins the ribbon for being the creepiest Pokémon ever.
A few other Pokémon are creepy as well. Grapploct is lowkey terrifying. The way it chases the player in the overworld in Pokémon Sword/Shield makes me want to avoid the water. Appearance-wise, it looks creepy whenever it opens its mouth. In addition, I always thought his cry sounded creepy, as if it should have belonged to a Ghost-type Pokémon instead of a Fighting-type, pseudo-Water-type Pokémon. However, I recently saw a YouTube comment that mentioned how Grapploct's cry sounds as if he's saying, "I smell cheese," which I can't unhear now. Shiinotic is another creepy Pokémon. What makes Shiinotic so creepy is the fact that, despite looking super cute and being a Fairy-type, a type often associated with goodness, Shiinotic enjoys ensuring you get lost in the forest before putting you to sleep with its spores and draining your vitality. In the process, it does it all while maintaining that creepy smile on its face. The Sinnoh legendary Pokémon Giratina is also creepy, mainly how he, she, or it lives in the Distortion World and, more recently in Pokémon Brilliant Diamond/Pokémon Shining Pearl, in Turnback Cave, both of which are creepy locations. I'm sure you Platinum players remember the cutscene with Giratina before the Distortion World part. Giratina also seems to be based on Lucifer, as an evil counterpart of Arceus, who is supposed to be based on God. That alone makes the thing creepy. Unova legendary Pokémon Kyurem is creepy because the entire town of Lacunosa is terrified that it would "steal" people and Pokémon, then eat them. Also, Kyurem's appearance is off-putting. Cofagrigus is also disturbing. That fact it has no problem turning people into mummies really made me think Game Freak was definitely attempting to gear generation V towards adults compared to the other generations. Finally, this probably might only be true for me, but female Pokémon that look weirdly humanoid creep me out to a degree, especially Pokémon like Gothitelle, Pheromosa, Jynx, and so on. Something about them just look . . . off, especially Pheromosa in Pokémon Refresh.