if you're looking for dark sounding scales try the locrian mode, thats about the most dissonant, I think.

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if youre not into harmonic/melodic shit - as mentioned, locrian. also, mixolydian may be considered a 'badass' version of the major scale, dont underestimate major sounds. but the cool thing about mixolydian is that its not used so much in metal, so you can get some really unique sounds by using it. Phyrgian can also sound dark if you use it the right way. if those dont work out you could always try regular minor, which would be the easiest to get the feel out.

most importantly, make sure your rhythm section is in whatever mode you want before even fucking with lead. cause if you are writing in a different key it might sound a bit off