Well if dual-typed moves are true, then according to this "inside source" there won't be many of them. How they work is simple in principle, but you have to get used to it and add more depth and variable to the type chart. Fire/Ground (Earth Power?) would deal only Fire on Flying type. Steel/Electric (Magnet Bomb?) would deal neutral damage to a Water type. Fire/Flying (Heat Wave?) against a Dry Skin Paras in Sun is bit tricky, but with a quick calc we can get: ( x4 (fire) + x4 (flying) ) x 1.5(fire under sun) x 1.25 (dry skin) = a whopping x15 damage. That'd make Heat Wave's power after SE calc and dual stab factored (Moltres, Charizard, Ho-oh) = 100 * (1. + 1.5) * 15 = 4500 WOAH. EDIT: I realize I'm making assumptions here, but I think this is the way it'd work if it was introduced. EDIT 2: I think dual-stab would be 1.5*1.5 instead of 1.5 + 1.5 making the damage 3375. still high XD. EDIT 3: yeah on second thought Fire/Ground would do NO damage on flying types even with fire as one of the types like Katakiri said.