Can someone explain how rock type moves don't affect flying type Pokemon?

Dec. 21, 2014

So I had a battle at the ‘Rating Battle’ and fought Mandibuzz and my Pokemon was Swampert. We were both holding Rocky Helmet and this is how the battle went:

Swampert move: Rock Slide, Mandibuzz move: Taunt(Rock Slide was super effective as usual then)Swampert move: Hammer Arm , Mandibuzz move: RoostSwampert move:Rock Slide, Mandibuzz move :Foul Play

When I used it here it had a normal Damage it wasn’t a " super effective" thenSwampert faint then my Aggron was next I used Stone Edge and it was also not “super effective"so can someone explain?

Pleaselog inorregisterto add a comment.

When using roost the user who uses roost loses its flying type for that turn. This means that Rock Slide would no longer be Super Effective against the Mandibuzz, because it’s no longer actually a Flying Type anymore.

Roost