I always hear on this site about eviolite. I don't know what it is.
An Eviolite isn't exactly what Firetyperuler said. An Eviolite Stone is a hold item that raises the Defense and Special Defense of a Pokemon that can still evolve by 1.5x. So, a Dusclops could use this item well, but a Dusknoir couldn't.
Source: Ask any professional battler that uses Chansey or Dusclops.