Rototiller is a ground-type move. All grounded Grass-type Pokémon on the field receive a one-stage boost to their Attack and Special Attack stats from Rototiller, with the exception of those that are using a move like Fly or Dig that grants them semi-invulnerability. If there are no Grass-type Pokémon that are qualified, Rototiller fails.
Have you ever seen this move before?