Slipknot is an American nu-metal band.
They are featured in Chapter Ten of My Immortal as a "goffik" band, though it doesn't really fit in with the other (mainly Evanescinze and MCR) supposed "goffik" bands, which are mostly emo. Though, given how Tara seems to think of Nrivana and The Beetlez as of a similar genre, it's not that aberrant.
Slipknot is also mentioned in a long list of goth bands present in Chapter 3: Duality of I'm Not Okay, which owes its name to their song "Duality".
Bloody Gothic Rose 666 sounds like a cross between Slipknot, GC and MCR.