hmmm... having whimsicott AND thundurus seems redundant.
i would recommend a no thundurus and just whimsicott.
i really like your drifblim with lucario idea. so DEFINITELY run physical set. but payback might be weird. because it is more powerful if you go second, and drifblim has a fair amount of speed.
and on politoed i would recommend this set:
Politoed @ Choice Specs
252 HP / 172 SAtk / 76 SDef / 8 Spd OR
252 HP/ 100 Defense/ 72 Sp attack/ 76 SDef/ 8 Speed
Modest Nature (+SAtk, -Atk)
- Hidden Power [Grass]/ Focus Blast
- Ice Beam
- Hydro Pump
The First EV spread lets it KO a ton of pokemon like metagross in one hit. the second one lets it tank more physical moves like fighting gem close combat from a hitmontop. this can also take a dragon gem draco meteor from a timid latios (both can take this) you want hydro pump and surf so you can either spam surf, or if you have something out with the more powerful hydropump and not hit your teammate.
Sorry But your gastrodon is just... >.< i can't stand it. putting a mix set is really weird in doubles. i would not ever think of doing special and physical moves on one set. and that set won't live anything. and i really think that zoom lens is really awkward. try this:
Gastrodon @ Sitrus Berry
Trait: Storm Drain
EVs: 252 HP / 108 Def / 28 SAtk / 120 SDef
Bold Nature (+Def, -Atk)
- Ice Beam
- Earth Power
This Gastrodon set is on the bulkier side, though it isn’t lacking in the offensive department. Gastrodon’s Defense stat is pretty average, so a Bold nature is preferred if you’re looking for a mixed defensive Gastrodon. Defensively, this Gastrodon can do a ton. It survives a Fighting Gem Close Combat from Terrakion and is only 3HKOed by Zen Headbutt from Metagross, Crunch from Tyranitar, and Bug Bite from Scizor. Draco Meteor Dragon Gem from Timid Latios doesn’t even KO while Sitrus Berry keeps Gastrodon from being easily picked off afterwards.
You really dont need scald or muddy water. you have 2 other pokemon with water moves. this guy is THE bulky gastrodon. the one you posted i checked can barely live any moves that would be useful to tank. and when i does it easily gets picked off by the next move.
also your whimsicott should either not have leech seed and not have leftovers and have focus sash, or just have protect to stall out. but i would recommend this:
EV's 252 HP/ 252 Spe/ 4 SP.Atk
This is a more practical set. leech seed is better on a pokemon that has bulk. and the only way this guy lives anything is with the focus sash. Tailwind is more practical because stun spore is very inaccurate, making it unreliable. you need giga drain because of the being completely countered by gastrodon. taunt will help take out any other prankster users (all of them are slower than this guy) and will shut down trick room setups and most cresselias.
Finally... Starmie? it would really be great if you still could give it a focus sash... but you really will need that on whimsicott. i would maybe put a kingdra or dragonite there. here are the sets:
kingdra @ life orb/dragon gem
Ability: swift swim
4 HP/ 252 sp attack/ 252 speed
-Muddy Water/ Hydro pump/ Scald/ Surf
This is the basic rain sweeping kingdra. this guy can take out so many pokemon with that monster speed. it can outspeed basically any pokemon other than excadrill in the sand. Draco meteor is deadly, muddy water hits both of them and the rain boosted power is great. hydro pump give huge power with the accuracy and not hitting both of them. scald is like hydropump but not as powerful and more reliable. finally, surf could work. boosting your gastrodon with it and hitting both is good, but hitting your own is a risk. Dont do substitute. since you dont have fake out it will be really hard trying to set that up.
Dragonite @ Yache Berry/ Dragon Gem/ Life Orb
78 HP/ 252 sp attack/ 180 speed
Complete Rain Abuse right here. Hurricane and Thunder are super powerful moves that get 100% accuracy in the rain. Draco meteor will do massive damage too. dont do dragon pulse for dragonite isn't powerful enough in general on the special side to use a move that weak. also it tanks everything almost with that multi scale. also, use protect whenever there is a pokemon with fake out so your ability isn't broken. The EV's let it outspeed a neutral speed nature base 70 speed pokemon. namely politoed and hitmontop.
But Starmie could be viable. only other thing is the bullet punch will be super viable on lucario. i just dont know which moves you should get rid of... maybe ice punch because scizor would be a bit of a problem sometimes without blaze kick.
Finally, Cresselia will tank out your team other than lucario which might get KO'd before being able to attack. You will really want a scizor on there. since i recommend not using a thundurus there is space for another pokemon
Scizor @ Steel Gem
196 HP/ 156 Attack/ 4 Def/ 124 sp defense/ 28 speed
-Aerial Ace/Acrobatics/ SafeGaurd/ Tailwind/ Feint/ Superpower
This Set can tank a max sp attack black belt cresselia hidden power fire OUTSIDE of the rain 66.6% of the time. In the Rain this set tanks a ton more fire moves. The 3rd move is interesting. you could use aerial ace, which gets the technician boost, and always hits. acrobatics is a bit weaker unless you have used your item already. only real drawback is not guaranteed hit. Safeguard is an awesome move. if you can't get a taunt off them amoongus might completely put your team to sleep. Tailwind is there just as another tail winder, which might come in handy. Feint will require some predictions, but it can break through protect and let you KO which can ruin your foe. also having two steel pokemon will be good for tanking those nasty dragon moves, and the fire weakness shouldn't be a problem. Superpower is just a powerful move that could be useful.
these are just the final touchups. but i love your team idea and think that it could be a great, probably winning team