It has Multiscale, so Roost is there for Multiscale abuse. Thanks for any suggestions =)
Well, you have Aqua Tail already, so I suggest Earthquake between the two.
However, if you are not using it in the rain, I highly recommend Fire Punch over Aqua Tail, as it hits Steels like Skarmory much harder.
I recommend that you teach it moves which are effective against other Pokemon my choice would Fly, Blizzard, Earthquake, Dragon Rage or Outrage, but be warned outrage makes your Pokemon confused.