Film: The Monster that Challenged the World (1957)
Height/Weight: Twice as large as an average human.
Summary: Giant lizards, giant spiders, giant apes, giant...snails? Giant snails. We can't tell which is weirder. Is it the fact that this exists, or that they made it menacing somehow?
History: The issue with Califonia's famous rift lake known as the Salton Sea is that it's located above the epicenter of the San Andreas fault. So when people start dropping test bombs on it, it only makes sense that it'll crack the Earth wide open. Perfect for some slumbering giant snails that have been breeding for this exact moment in time.
Notable Kills: Nothing special, especially since a certain upcoming cave-dwelling arachnid has done the "horrifying shriveled up prey" thing better.
Final Fate: After some escape into a nearby canal, they are all blown up. One that hatches in a lab is assaulted by a fire extinguisher before being mowed down by the authorities.
Powers/Abilities: None except good mandible and body strength.
Weakness: These snails hate cold temperatures, and cannot develop in the egg properly in these conditions. Also, anything conventional.
Scariness Factor: 3.5-The ghastly face and sheer size of the deep-sea gornaxis makes it a sight indeed, but they're a little too easy to kill for them to "challenge the world" necessarily.
Trivia: -As the film helpfully informs us, there are indeed snails that won't settle for your garden as food. The kicker is that most of them live in and/or near the ocean.
-The largest snail is the African giant snail, which is also another phrase for "overgrown invasive meningitis-spreading property-damaging slime monster".