Ok I was training my Noctowl and was fighting a geodude when it used Magnitude (6) and it hit my Noctowl. The previous turn i had used Roost. Umm...how was my flying pokemon hit by a ground attack? Am i just stupid or what? Does roost have anything to do with it since the attack said the user "lands?"
Um completely unnecessary comment!
And roost has that advantage as it completely removes the flying type during that move so a noctowl used roost before the opponent and then the opponent used and ice attack. That Ice attack would not be super effective because noctowl at the time had lost it's flying type.