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IMO Flygon is the best candidate for the scarf.. CS mixed sweeping set is my favorite Flygon set. Porygon-2 or Porygon-Z would also serve well as a scarfer I think.
Maybe Rampardos..
Does focus sash work twice?
Example: I send in pokemon #1, it gets KO'd, focus sash activates. I roost (opponent doesn't attack xD - it's just a stupid example), switch into #2, wishpass to the first pokemon, so HP is full again. If #1 gets KO'd now, will focus sash activate once again?