An attacker and sweeper are pretty much the same thing, they focus on dealing heavy damage on the foe, examples of them are Rampardos, Salamance, or Chandelure. Defenders & Walls are there to buy time against the foe, most of them all know toxic to wear down the foe, some also know thunder wave. they can also to be used to protect your teammates or use heal pulse to heal them, but they are generally called supporters. examples of Walls Are: Dusklops @ evolite, Shuckle, or registeel. examples of supporters are : Blissey, Slowking, or Alomomola.