#1
What scale is this that is used in quite a few metal songs...if your guitar is drop tuned to drop D these notes are in it on the low D

----0-1-3-5-6-8-10-12------

plugged it into the scale calculator on jguitar.com (awesome site) and couldn't find one that worked. thanks!
#4
D Eb F G Ab Bb C D

looks like C minor. could also be Eb major. in this STRICT sense, you have D locrian, but i highly doubt it's being used as such.

remember -- what a scale REALLY is depends on how it's used in a composition. however, if you're just given this set of notes -- starting and ending on D - you've got D locrian.
Anfangen ist leicht, Beharren eine Kunst.
#5
The thing with a lot of metal is that it doesn't follow a handful of theoretical standards. It uses shapes like the locrian mode without using them in a modal sense, which is why so many people don't understand modes correctly. I'd just consider it as the D natural minor with the 2nd and 4th flattened, because that's what it is, though it adheres to the shape of D locrian.

The phrygian shape's very prominent as well (natural minor with flat 2nd).
modes are a social construct