Elise
For sure, I have arachnophobia and I'm easily scared by even the smallest spiders. Now spiders in pictures and videos don't often make me scared, but for some reason they make me uncomfortable and itchy all over my body. So seeing Elise either makes me scared or real uncomfortable, so that's fun.. /s
Her "human" form is okay I guess, but I feel discomfort when she's in her spider form. And I hate her ult, because it's a huge spider jumping..
One time when playing Aram the camera kind of bugged when Elise ulted, and I saw the ult kinda up close, and it genuinely looked like the spider would jump out of my monitor, like damn that actually gave me a heart attack.
Rengar
has also jumpscared me a few times in game, I still remember wanting to ward a bush while the enemy botlaners were gone, and him jumping out of that bush, I really didn't see that coming haha.
This guy is also pretty scary in my opinion, now you have his look and way of moving, which I guess kind of resemble a spider, but his ult is really dark..
I don't know much about Shaco tbh, but the splash arts of all his skins are creepy.