Misty Bog in the first game is populated by the above-pictured killer plants that sit idly by in groups before Spyro approaches them. Should he come within several feet of them, their already visible eyes fixate on Spyro and their leaves rustle. When Spyro edges any closer, the plants charge at him with gaping maws and yellow fangs.
In Misty Bog, there are these enemies called Attack Frogs. To put it more clearly, they're light blue frogs that will lash at you with their extremely long tongues if you get within ten feet of 'em! They hop around carefree, but there is always malice in their eyes.
Whenever you can hear something, but can't see it, like, for example, when chuckling thieves are hidden out of view and when the trembling of the petrified dragon on a floor above in Haunted Towers can be heard (and the dragon is really tough to find).
Dark Passage, the place where nightmares are literally made, as it's the scariest world in the Dream Weavers' set, and it is called "Nightmare Road" in the Japanese version of the game. It is populated by critters that, though tiny, adorable, and mostly harmless in the light, transform into hideous beasts in the dark. The armored turtles become invincible and get some fangs, and the puppies transform into giant red hellhounds with evil red eyes and gigantic mouths lined with razor sharp teeth. If Spyro walks near one of the devil dogs in the dark, he better be ready to breathe some fire, because if he doesn't the demon will pounce on him with incredible speed, devour him, chew him up, and spit him back out. As for the turtles, their heads grow as they spit fireballs. Not as bad as the dogs, thankfully.
In the High Caves in Spyro the Dragon lurk giant metal beetles ready to chase Spyro down should he be daft enough to set foot on their ground. They are fast, invincible to standard attacks, and they have a tendency to hide just out of view. At one point, Spyro must dash past a couple to reach a powerup that allows him to kill them, and it is one of the most tense parts in the game.
The Doctor Shemp boss level of the first game comes with strange little tribal beings in huge faceless masks, who run at you screaming on sight, sent by their Brawn Hilda-esque "wives" (whether you'd noticed them first or not) via bitch-slap.
You can flame them, but if you dodge them, then they delibrately run off the bottomless edge. Their falling screams don't help matters in the slightest.
Any enemy could just about give you a heart attack if you managed to get close to them without having them come into the frame - enemies only attacked if they were seen by the camera, so if you landed right in front of them and waited for the camera to catch up, you'd end up being ambushed seemingly out of nowhere. There's one spot in Misty Bog where this is very easy to do with the above-mentioned killer trees. Jump down a log facing a certain direction, and their leaves will rustle in anticipation until the view swings around...
Spyro 2: Ripto's Rage!/Ripto's Rampage!/Gateway To Glimmer
The plants from Misty Bog in the first game get their expy in the ravenous bushes in Fracture Hills, in Spyro 2. They act mostly the same, but without the fangs. On the other hand, they look just like all the other bushes, which aren't alive, until Spyro approaches them. This way, their attacks are more startling, but not quite as scary.
The poor caveman shown during the intro in Skelos Badlands. He gets his ass set on fire by a Fire Wizard, then gets picked up by one of those catbats, and gets dropped down a bottomless pit. Worse yet, the Catbat LAUGHS.
Spyro : Year Of The Dragon
Spyro: Year of the Dragon upped the ante with the Nightmare Fuel: for starters, the Sorceress turns minions into bosses to fight Spyro (akin to Kamek in Yoshi's Island). At least one was forced into it, despite struggling and pleading for mercy.
One has to think, was he resisting because he didn't want to become a monster, or was he resisting because he knew he was being forced into a fight he couldn't win?
The Dino Mines level in Year of the Dragon is teeming with gunslinging, dynamite-flinging dinosaurs with loud roars and attacks that are quite difficult to avoid. Even at a distance, the blue ones roar at you with dynamite in their mouths, prepared to spit it out.
In Evening Lake Home, there is an egg hidden inside a small whale. The whale itself is not unsettling, but the way he gobbles Spyro up can be startling the first time.
In Spyro: Year of the Dragon, the Evening Lake world Frozen Altars has a lot of giant snowmen that Spyro must defeat with lasers; getting too close to one results in them grabbing Spyro, shaking him and throwing him away. All while sporting a demonic Slasher Smile.
Lost Fleet: a world full of broken, abandoned ships. Its inhabitants are rhynocs wearing ghost sheets and huge crabs, and it's surrounded by pools of acid... what the fuck happened to the crews?
The sorceress is arguably the worst of the antagonists. She's not terribly humorous like the other villains and her goal was to kill 300 newborn dragons in order to get their wings and become immortal. She even said it wasn't necessary to kill them but it'd help keep them from their squirming; if she didn't kill them though that'd still be nightmare fuel in the form of Cold-Blooded Torture.
Other instances outside the first trilogy itself
The full-bodied sheep muppet with burns all over his body as well as a sinister looking scowl can give people, especially little children, nightmares, even though he was intended to be funny. The three commercials he appeared in: the first,the secondand the third, all of which described in this documentary.
Spyro: Enter The Dragonfly has a rather spooky glitch in which everyone goes all slow motion-like.
The Tower of terror in Spyro: Enter The Dragonfly is pretty scary not just because of its faces that spit rocks and darts but also because of the large orange realistic looking spiders crawling on it.
This Troper was walking down a cave in Spyro: A Hero's Tail's Crocovile Swamp and then a spider jumped out through a seemingly solid wall.