Dugtrio has the potential to be a crazy Volt Switch-focused trapper (or Offensive trapper in general). Earthquake and Sucker Punch are great offensive options. Smack Down has potential to have amazing synergy with Arena Trap, being able to ground Levitating and Flying mons like Zapdos and trap them. Fourth slot can use anything, Mud-Slap would be a good filler option to make Dugtrio harder to hit or Stone Edge for more damage. Assault Vest can be used if Dugtrio isn't using Stealth Rock.