tons of light heros (4 & 5 star) going to drop from the rare machine right now, should last until the 18th (Friday?). i've not yet figured out what masks are used to evolve. Knights/goblins/ogres I think?
I managed to clear the emerald dungeon once, rank up off of the dungeon, then immediately clear it again. First run I got 5 of the base green dragons (which I fed to my toyceratops), second run was 2 base, 2 high, and 1 king!
Which color dragons, the starter version ones? Yes keep those. Keep in mind you get a "gift" pull that will drop a start dragon for you and a friend (and you should trade that with someone else who has one, so you can get two dragons).