>>23228909He has one thing that the others don't have: Encore. That, combined with Infestation, Toxic/Endure, and Custap-Destiny Bond (Gluttony ability optional, but encouraged), can trap and take out enemies locked into support by whittling their HP down, or those locked into an attack with Destiny Bond.
Can usually take out a good one or two of your opponent's Pokemon. No one knows how to react to a Swalot.