First off, i'm loving this team just for the Tankchomp + AV Metagross core and my beloved Hydreigon.
There are by the way some things i'm concerned about:
1) You should change Hydreigon to a full special set imo, while i can see why you're running U-Turn btw. It's true that with this EV spread it can OHKO mons like Ferrothorn and other sutff, but you'll feel the difference against neutral opponents, plus i don't see a Dark STAB. To avoid this try this set:
2) BP on Metagross is just for priority, you could run Ice Punch for Ground coverage and the 4x weaknesses stuff but the most common Ground Type moves abusers are TTar, Exca and Hippo. TTar and Exca are checked already by EQ and a no STAB Ice Punch on the third one doesn't provide enough damage. Plus, the 4x weaknesses are covered by the rest of your team, especially Starmie and Gon. Aside that, the rest is good.
3) Pretty smart idea on Chansey, i really like it despite the fact that i hate that useless pinky thing. Worst-case scenario, if you're against a Special Attacker that's
able to have some sort of recovery and has been statused already by Starmie's Scald (I.E. a Milotic switched into your mon) then you're in trouble as all you can do is use Soft-Boiled. Then you can do 2 things:
- Replace Scald with Hydro Pump to have a lot more power (wich could fit Starmie's role better) and keep Chansey this way
- Replace Counter with Seismic Toss, to have other ways to damage your enemy
The rest is fine, as i said before i like this team a lot.