- Medusa. Sure, it doesn't actually kill you, but still...brrr...
- The Leviathan aliens. Not only can they control your mind, but if they actually transplant their consciousnesses into you, you'll end up slowly physically mutating into one of them.
- -and when they're forced out of you at that point, they pretty much put you into a debilitating coma.
- They turned out to be just escaping from C-Rex, but the mutant giant squids seen in the first two episodes are pretty scary, especially how they first appear as random tentacles coming out of the mysterious tar to grab people and pull them underwater.
- The Silver Hydra, a colony of small silver microorganisms that "freeze" their prey. The first victims after waking up? Kids.
- The Crackler, a physical projection of a soft-spoken man's repressed tension going on a rampage with the intent on attacking all of the man's stressors. Then there's its laugh... if you can call it that.
- The DNA Mimic. Picture a puddle of liquid DNA that can replicate any living thing it comes in contact with. Then there's the weapon that was used to kill it, nitric acid, or at least scramble its structure: a solvent capable of melting any living thing right down to its molecular structure.
- The episode "Future Shock" has the team travel to an alternate future, where monsters know as D.R.A.G.M.A.s have destroyed the militaries of Earth and basically overrun the world. When Nick hesitantly asks what happened to Godzilla, Future Craven can only sadly point to a memorial, stating that although he fought to the last, the monsters finally overcame him. It's chilling to think of monsters able to kill even Godzilla himself.
Nightmare Fuel / Godzilla: The Series