pentatonic was used heavily in thrash, particularly Em
There's no such thing; there never was. Where I am going you cannot follow me now.
Natural minor, harmonic minor, minor pentatonic and E monotonic . Make liberal use of accidentals, particularly a minor second above the tonic, not to mention a major sixth above the tonic for use in power-chordifying the (major) second degree. Pretty much that, I think. Oh yeah, some tritones never hurt...except when they do.