Fridge Horror: Uzo and Muzo are the villainous version of Those Two Guys. Yet, they are the last people of Mt. Gokuho. So when Shinbu kills them both in revenge, he has, essentially, killed off an entire clan. Them being total assholes could mitigate this a bit but still...
Nightmare Fuel: The Toshintetsu, especially because the long-term fates of the souls trapped inside are not openly explored. We don't know if they are aware of their suffering, helpless, forced to provide insight from the terrible machine.
Honestly, the premise of The Glory Festival and Seima technology is sufficient nightmare fuel.
Byakko: He moves too fast for you to land a hit on him. He hits like a truck. And he can poison you and cause sickness.
Seiryu and Densei: Seiryu hits like a truck, and his electric attacks can really hurt you. Doesn't help that Densei is off to the side, unhittable, preparing his laser spam attack. When Seiryu goes down, Densei fights you one-on-one. Unless you're on the New Game+, you won't be using any Kirin Chi attacks since you can't learn it until AFTER the fight. He is a pretty quick fighter, to boot.
WTH, Costuming Department?: Take a look at Lu Yan and Li Yin's shoes. There's no possible way they can have their heels up with those, never might be able to fight in those clogs.
The Woobie: You have to feel for Sui Lin. Not counting Shinbu, she's the last disciple of Seiryu and witnessed the massacre of her clan. Much later, she falls victim to Chi Disruption, twice. She felt incredibly scared about what she did and fears what would happen if she were to fall into it again. The second time she fell to Chi Disruption, she killed Jok Xiu. When she recovered from it, it almost absolute broke her. She then gets captured by the Kirin. Densei was about to play some mind games on her before Shinbut put a stop to it. She goes through a lot of crap in this game.