Err...

Guys & Gals... that's NOT the "Lord of 
Nightmares".

That is Hellmaster Fibrizo from Slayers Next.

Um, this is a HUGE HUGE SPOILER so beware:

The Lord of Nightmares looks like Lina Inverse, 
at least that's all we have seen of "it" other 
than a brief flash of the guy/gal with the long 
blonde hair in the Slayers Next opening sequence.

Lina casts a huge spell to stop Hellmaster (the 
guy in the cel on Yahoo Japan) because he had 
just killed all her friends pretty much (Zel, 
Amelia, etc.) She ends up taking the Lord of 
Nightmares into her own body, so the LoN looks 
like LINA but she turns into a golden color all 
over her body.

I know a couple people have cels from this scene 
(Katy?) so hopefully someone will post their cel 
of Lina possessed with LoN.

Below is a picture of LoN from the opening 
credits of Slayers Next.

Misa ^_^;