Some of the scare tactics employed on the test dummies. Particularly the ones employed by Terri and Terry Perry, assuming a Slender Man-like shadow silhouette, and by Squishy, sneaking up behind and providing an unsettling Jump Scare with his creepy staring.
The Roar Omega Roar Fraternity's tactics aren't to scoff at either. Special mention goes to Johnny whose roar is comparable to Sulley's.
The members of Python Nu Kappa may seem like bubbly, cheerleader-esque girls, but at points in the film, they provide a Jump Scare by baring their fangs and making their eyes glow red. That reminds one of succubi...
It is stated in the essential guide that the PNK girls are looking for jobs AT THE CREMATORIUM!!
When Sulley is practicing scare tactics and makes the jazz clown, it's truly unsettling.
And when Professor Knight was quizzing Mike on the different types of scaring techniques...imagine if a more frightening monster adopted those techniques...
Sulley is shown practicing one of them later, so there you go.
While Dean Hardscrabble "tests" Sulley in the Scare Exams, she mentions that a wrong scream would mean more than toxicity from a child. If a parent learns about the existence of monsters, it would be the end of monster civilization. Being a Scarer just became a whole lot more terrifying, something along the lines of a nuclear technician having to operate the cooling rods by hand, every minute having to utilize a completely different strategy, and the slightest slipup could mean disaster.
Dean Hardscrabble, the Dean of the School of Scaring. She looks like a centipede combined with a dragon...and one has to wonder how she would look like when she's scaring kids...
Even Professor Knight, who states that he doesn't scare easily, has obvious fear on his face when Dean Hardscrabble arrived.
The Eta Hiss Hiss Sorority. (or better known as HSS in the film) Goth look, spikes and piercings...and apparently Dean Hardscrabble was one of its members before she became the Dean of the School of Scaring. When their Sorority's name was announced in the Scare Games, the leader Rosie Levin, let out a hiss (pun intended) that was unsettling like a snake...
Word of God states that Rosie Levin has a black belt in Chew-jitsu.
Just...this. This is the scene where Mike scares the scare test dummy. And it is, actually intimidating! This is perhaps the ONLY TIME Mike Wazowski came off as actually SCARY! How scary? That's HIM in the image for this page.