* HighOctaneNightmareFuel
** Yeah, just at the first episode an old man who supposed to be dead resurrected... wait, that's not an undead, it's like something from.... oh my! EldritchAbomination!
** And don't get us started with [[spoiler: Oswald Lenn Mathers]] in the fifth and sixth episode, who is a formless monster that can use any demonic form he desires...
** Fin Cruda in the last three episode, along with TheDragon, is what could be described by this troper "If Giygas has human form"...
** Then there's the [[BigCreepyCrawlies giant, floating larva]] in Sekiren's debut episode. (shudder) Coincidentally, it actually does have the power to cause nightmares in the show itself.