Highly recommend for everyone to learn about the Harmonic Minor Scale. One of the biggest tricks up my sleeve that I use in solos and leads, definitely my favorite scale. I first learned about it by studying Syn's playing and note choice. Gives it a great, almost evil (dare I say sinister) sort of sound. Also sounds great on a nylon guitar and used in spanish/classical music.
It's definitely one of the key flavors to the Avenged sound. I noticed Syn seems to use Phrygian Dominant type motifs when he's doing his live solo breaks - it's so clever cause they don't sound like typical cliche cheesy metal Phrygian dominant leads one of my favorite things about his style