Keep in mind that a lot of these I have no real explanation for; they're just the first songs to pop into my head as I sat here and thought about conversations with each person. In other words, except where noted, don't read too much into it.
The Creature -- She Blinded Me with Science, by Thomas Dolby
Underdog -- Eye of the Tiger. Must be because like Rocky, he's an underdog.
Wolfie -- Bark at the Moon, by Ozzy
Tripod -- Semi-Charmed Kind of Life, by Third Eye Blind
Ghostie -- Your Number is One, by Rollins Band
Dirty Girl -- Mr. Scary, by George Lynch. Not because she's a mister, but because she, like this song, kicks ass.
Mistress of Horror -- Fully Alive, by Flyleaf
HorrorQueen -- Little Sister, by Queens of the Stone Age
hellrat -- Push It, by Static X
Scavenger of Human Sorrow -- like I told him way back when, his name always brings to mind Harvester of Sorrow, by Metallica
Cap Howdy -- Anarchy in the UK. Must be because he's a Brit.
I'll post more as they come to me.