Together with the RE 4 Regenerator.gif the best nope enemies around. I'm still at the beginning of Dark Souls (yes, I suck that badly. I need to play it again) and I still remember foolishly pressing on in this area, because I thought this was the path I needed to take to get somewhere. So I enter the cave, see shit flaring up and I'm like "well this was a horrible idea OMG GET OUT".
Other enemies that make me go nope every time:
- Lisa Trevor in REmake. The first encounter down in the cabin is simply amazing and creepy at the same time. The underground thing? Nope. Nope Nope Nope.
- "It" from Resident Evil 4. Sadler is punking you man, he doesn't have this weird thing in store for Leon. He's having a senior moment. Then you see the hanging cage structure and WHAM there he is. When you start and he's nearing you... oh god please go away.
- Creepy girl ghosts in Project Zero/Fatal Frame. I'm not easily scared, but Project Zero makes my skin crawl. Every time I heard something, I'm got all jumpy and yep there they are, ghost kids coming to haunt me. Aaaarrrggh.
Or this
Edit: bonus, zombies in ZombiU. To be fair, ZombiU together with Dark Souls is the definition of NOPE, but certain areas are just fucked up. One point in particular is just pure freaking evil. You enter another underground where everything is pitchblack. You pick up a flare and you see like six or seven zombies looking right at you. NOPE