This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Ruins
There is a very good reason why the locals maintain such a strict perimeter around the ruins... too bad the protagonists don't learn why until it's way too late.
The plants themselves are clearly nightmare fuel for the locals. They're mobile, carnivorous, and infectious. If you touch them, well, you're boned. Anyone that touches them gets a prompt Mercy Kill - or is simply herded to the top of the ruins to wait for the plants to do their work.
The scene where they search for the "cell phone" by following the noise, before realising it's the plant mimicking the noise to lure them closer into a trap.
When the plants start mimicking Stacy with all of them saying "I want to cut it" over and over and over again as she is filleting her own leg.
The amputation scene. It goes on for a very long time, with characters trying to smash and splinter gristly bone after the rest of the surrounding flesh has been hacked away - with no anesthetics whatsoever. To prevent bleeding out, they try cauterizing the wound with a pan that had been sitting on a fire. The character dies anyway, because they left him by the plants and were too busy arguing to notice what was going on.