Hi that's a nice offense team, that's the kind of teams I like to rate !
However, I can see some things you could improve considering the weaknesses.. Which ones ?
Here I go for the weaknesses :
- I think you're in bad
bad situation against another offense, especially the Deoxys-D ones. You can't really contain them from putting hazards bar killing the Deoxys-D in two turns with Politoed. And then, you're locked, someone will set-up !
Your Donphan won't be able to spin against a Gengar and will even get killed 1v1.
- I see
Rotom-W walling a good part of the team and dealing serious damages. Toed is forced out by volt-switch and your Electric resistance take a big chunk from any Rain Boosted HPump
- You're
pretty weak to Sun teams. Your offense usually don't like to fight too much for the weather. On the other hand, Sun teams are built to fight for their weather. Thus, you'll have to deal with a Venusaur under sun.. and I don't see how you can do it. Especially when we know how Donphan is hard to use against a classic sun.
Let's stick to that for the weaknesses.
My changes :
- A pretty classic change for any Rain offense,
Terrakion lead over Donphan. This way, you got a fast Taunter to beat Deoxys-D teams, and to put SR asap. Which is really important in an offense.
Moreover, you got a last resort check to Volcarona, which is always good to have because many pokemons here will have issues beating a Volcarona under the Sun.
Minor changes :
- On Politoed.
Switch Psychic to Ice Beam, you're not weak to Toxicroak at all, you will prefer the Ice Beam coverage. And it's really hard to catch a Croak on the switch when you get locked right after. You can't afford that in an offense. You can't let a Dragon rampage through your team like that.
Or you can change the item (Splash Plate, Water Gem, Expert-Belt..), but at least get Ice Beam on HP Grass.
- On Thundurus.
Give a shot to the Agility set. Agility on your last slot and you're good to go for a easy sweep.
- Gyarados. You really need a way to hit bulky grass and Venusaur, Volcarona, Keldeo harder. To me, a
Bounce set is just what you need for a late game sweep. Now that you got Terrakion as Taunter, play a Sub/DD set with Bounce and WaterFall as offensive. You're less prone to be revenged by a Rotom-W with a Substitute set.
THE SETS :
...

Terrakion @ Focus Sash
Justified
4 HP / 252 Atk / 252 Spe
Jolly Nature
- Close Combat
- Stone Edge
- Taunt
- Stealth Rock
Putting SR fast will help you so much against a Sun team to pressure them (like set-up on Forretress with Thundurus-T !)

Gyarados @ Leftovers
Moxie
56 HP / 248 Atk / 204 Spe
Adamant Nature
- Substitute
- Dragon Dance
- Waterfall
- Bounce
That's all ! Good luck with your team !
TL;DR