This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Travels Through Azeroth and Outland
Vizier Merun’khet might be the premier example in the travelogue. Formerly a nerubian vizier, he fell victim to the Scourge infesting Azjol-Nerub, only to be "resurrected" by a Forsaken scouting team. This resurrection consisted of forcibly implanting his brain into a human corpse. Not only that, but the shape of his brain doesn't really fit, so the gray matter is bulging out of the scalp. Imagine what it would be like if someone transplanted your brain into a giant spider, and you might have some idea as to how he feels.
The Shadowsworn and their dreadlord in the Blasted Lands, mostly by virtue of their bizarre behavior.
To elaborate, these cultists dance and party all day, forcing anyone they happen upon during their travels to join them, giving them a new name and forcing them to stay. Some even have horrible blisters and sores on their feet, but are oblivious to the pain. Then, when they reach camp, they all just drop where they are and go to sleep. Not all of them wake up though, having danced themselves to death, and the others don't even notice that they're gone.
Lady Tsavrash is a naga encountered in Azshara. The writer interprets the naga as being supremely arrogant, to the point that their nobles refuse to dirty their tongues by speaking the languages of the surface races. To communicate with landlubbers, Tsavrash uses a blind, crippled, and mutilated orc slave to act as her "mouth."
The Auchenai in Terokkar Forest have a particularly disturbing interpretation of the draenic desire for community.
There are a few entries—Silithus, for one, and all three sections of Zul'drak—that are just creepy overall.
The Second Entry on Terrokar Forest, featuring the Arakkoa's illusionary city...