I would pick flatter stages against a Mario. The platforms would mess up dair auto cancels and its followups. Plus, Mario gains more from platforms than Cloud. Your giant nair is pretty decent against Mario when he is offstage. Although I would avoid challenging him when he is already close enough to ledgesnap with upb. Try to learn the timing for two frame punishes by using dsmash facing away from the edge though. It could catch them off guard and possibly stage spike them. And if you are on stages with edges that are very pointy like Battlefield or Lylat, you can try learning how to dair through the stage for a spike or to hit Mario during the two frame window when he grabs the ledge. If you're daring, you can try and runoff fair since it has a lasting hitbox or backflip off the stage and fair to try and catch a low recovering Mario safely.