As CGI has adapted and improved in the modern age, a filmmaker's ability to create terrifying visions from their deepest nightmares has become more possible. While some would argue that this takes away from the realistic nightmares that were created by practical effects in movies like John Carpenter's The Thing, there are nevertheless CGI creations that stay with us long after the movie is over. While practical effects have their place, they have trouble creating the same nightmarish monstrosities that modern CGI can make.
Everyone can remember the first CGI monster they saw as a child, from the T-Rex in Jurassic Park to the Lake Monster in The Lord of the Rings. While some CGI monsters have ended up being relegated to bad memories for being more laughable than scary, and some have been scary for completely unintentional reasons, Rebel Wilson in Cats, for example, there are many that stay with you, left behind until you close your eyes and are haunted by visions of terror.
It is undeniable that horror thrives on awakening your darkest terrors, and CGI allows just that. Recently, this has gone further, with things previously impossible being done within the horror genre.
Some creations, for one reason or another, are truly scary...