Dewgong! I always loved this... Whatever it is.
It's got water typing, and a rain supporting ability! So it looks pretty positive from here.
Dewgong (M) @ Leftovers
EVs: 252 HP / 252 Def / 4 SDef
Modest Nature (+SAtk, -Atk)
- Ice Beam / Toxic
So this is a staller / tank set.
Stockpile is fun with defenses, a poor man's Cosmic Power.
While Surf is STAB, and rain boosted.
You can have Ice Beam for more STAB, or Toxic for some stalling ( I prefer toxic )
Dewgong (M) @ Life Orb
EVs: 252 HP / 252 Atk / 4 SDef
Adamant Nature (+Atk, -SAtk)
- Icicle Spear
- Iron Tail
Icicle Spear is STAB, breaks subs, and can hit up to 125 power.
Waterfall is STAB and rain boosted.
Rest recovers you with no wait, due to Hydration.
Iron Tail is coverage.
Overall, he's pretty good. Shallow movepool makes him harder to use though.
Rating in the rain - 6/10