I really like Nightmare,if you want to know the story behind him you should play Soul Edge. He was a soldier's (knight) son who wanted revenge for his death,but to do this he needs a powerfull weapon (soul edge). So he wanders the earth defeating everbody on his way till he meets up with cervantes. He defeats him and the 2 short swords become on (soul edge). Right then he becomes the black knight also known as Nightmare.
There's only 1 thing to do: to find the man who killed his father....little didn't he know that HE WAS RESPONSABLE FOR HIS DEATH. After searching years...he finally remembered holding his father head in one hand. Siegfried was once a member of bandits and attacked his own town,he never intended to hurt anybody...but the captain of the town (his father) went after him...so he killed him.
Finally knowing this,he became more insane and the soul edge corrupted his soul....that's the story of Nightmare.
Inferno is just the spirit form of Soul Edge....so Nightmare really rules.
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