This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / 30 Days of Night
The vampires themselves are soulless, sociopathic predators that look like human sharks and know exactly how to cut off their little snack bar from any chance of escape.
The vampiric little girl.
The situation the inhabitants were in was utterly chilling because there was just no way out and more importantly, those vampires are among the scariest and meanest. Quick, strong, silent, predatory, sadistic, cold. The worst might be that characters one really cared for got changed into vampires. Nightmare & Heartbreak all in one.