- Mumm-Ra, period.
- In the first episode we witness the destruction of all but one of the life ships which escaped a doomed Thundera. Leaving only a handful of Thundercats alive. At no point does the series delve into the horror of an entire species of that many men, women and children being wiped out.
- As creepy as Mumm-Ra was, the Living Ooze was definitely the scariest thing on the show.
- A nightmare-tastic episode has Lion-O was trapped in some creepy catacombs with these Morlock-esque creepers with gigantic eyes, speaking about how they had been driven out of the world by people being too terrified of what was written in their books.
- Worse, their intention of kidnapping Lion-O and forcing him to read to them until his eyes become useless.
- Tygra becoming addicted to the Keystone, becoming both paranoid, insane and losing a lot of weight along the way. For an 80s cartoon to depict not just the mental but also the physical damage addiction - any addiction - could do to someone, and do it so graphically, is as impressive as it is creepy.
- The wild and crazy dream sequence Tygra had when he got hooked on the Silky Fruit is also pretty damn creepy.
- Whilst navigating through the cave of the Nether Witch, many strange, eerie figures were encountered; amongst them, an infernal hand kept appearing with a dissuading gesture, as if trying to warn Lion-O not to proceed further.
- From the last episode, a giant turtle attacks Bengali and Snarf, but first, it opens its mouth...
- The Mad Bubbler's victims are driven mad and compelled to endlessly fight. In their last moments of sanity, they are explicitly told of their fate and shown the remains of those before them.
Nightmare Fuel / ThunderCats (1985)