I'm sorry, but if you want to keep sun, you really should drop Whimsicott. Most of the time it's easier to switch around then use a turn setting up. Whimsicott was a great Pokemon in 2011 because 99% of the time it stopped priority Thundurus/Tornadus which were on 99% of the teams, but they aren't nearly as common anymore. I'm going to agree with Zog and replace Whimsicott either with Nintails, which at least has good damage output, or just forgo sun entirely and replace Shiftry too. Half of your team is also Garchomp weak, with literally nothing that can OHKO it. I would suggest replacing Shiftry with Latios (OHKOs and outspeeds the common Garchomp) and Whimsicott with either Nintails, or a rain counter such as Gastrodon or Thundurus.
Terrakion will never use X-Scissor, and it doesn't OHKO anything, so you should replace that with Quick Attack. Priority is always useful.