Here is a rain team that I've been working on. it centres around para-fusion Jirachi with sub and defeating the few things that can stand up to it. Jirachi himself has been extremely successful but the team has been falling apart in most of my matches, mostly because I'm constantly having trouble winning the weather war.
Jirachi @ Leftovers
Serene Grace
Quiet nature
252hp/252spatk/4spdef
-thunder
-iron head
-water pulse
-substitute
This Jirachi is a total ass under rain, on top of having enough hp for his sub to survive seismic toss and losing his fire weakness he has a 120 bp move with a 60% paralysis chance, a pseudo stab on water pulse which has a 40% chance of confusion and of course iron head is a decent stab with a 60% chance to flinch. He gets a sub up ridiculously easily because of his great bulk and steel typing. Assuming he gets a paralysis with his thunder which he's likely to do the opponent only has a 75% chance to move. If he's confused he only has a 75% chance to move divided by 2, and if I'm using iron head take that and subtract 60%. It only gets worse if they're using a less than 100% accurate move and/or can't break my sub with 1 attack. His attacks also have decent synergy with each other and special attack investment means I deal decent damage while haxing the opponent.
Politoed @ choice specs
drizzle
modest nature
252hp/252spatk/4spdef
-hydropump
-focublast
-hidden power [grass]
-ice beam
Politoed brings the rain and provides some immediate power to the team, he does a good job forcing out all the other weather starters assuming he comes in on them and can nail 3 of the 4 with a super effective coverage move as they come in. Hidden power grass mess up water grounds like gastrodon as well as lanturn who mess Jirachi's shenanigans up. He also does decent damage to Ferrothorn who also walls Jirachi, especially since iron barbs hurts more than iron head. he also just barely survives standard genesect's thunderbolt even at +1 and KOs back with hydropump.
ferrothorn @ leftovers
iron barbs
sassy nature
252hp/88def/168spdef
-power whip
-stealth rocks
-leech seed
-protect
Ferrothorn is a boss, no questions asked. I added him to better take dragon attacks because of his wonderful mixed defences. I run leech seed for the passive damage and recovery and protect to exploit it, the one extra turn can often make the difference in a match and the nice little boost from seeds gives me a bit of leeway for his replacement when he switches out. I elected to run only stealth rocks because I would rather be able to set up quickly and it's better if for me because they hit every pokemon not just grounded ones. I also didn't have to be very centred on my spin blocking because it's easy to set them up again and again. Power whip has slightly better coverage than gyro ball and gives me an additional way to break bulky waters.
Jellicent @ leftovers
water absorb
calm nature
252hp/36spatk/220spdef
-surf
-shadow ball
-ice beam
-recover
Jellicent joins with Ferrothorn to create the famed ferrocent defensive core of hazard laying and spin blocking, resisting 15 of the 17 types together. because Jirachi excels with paralysis support a status spreading Jelli would clash with that, instead I run a 3 attacks + recover bulky attacking tank. Surf and shadow ball are stabs while ice beam is simply a phenomenal attacking type in general and pairs nicely with water to hit the grass types that resist it. Jelli's also great at tanking special attacks and provides a useful fighting immunity.
Rotom-Wash @ leftovers
pressure
modest nature
184Hp/4def/144Sp/176Spe
-hydro pump
-volt switch
-pain split
will-o-wisp
Rotom-Wash pairs with FerroCent quite nicely, resisting flying and being immune to ground- the two types that hit Ferrothorn and Jellicent both neutrally make it a great partner. It does sadly give this team a third grass weakness however with 3 resists, two of them being double resists it's nothing that can't be dealt with with smart switching. Rotom also provide utility in volt switch however he has no u-turner to join with. He does decent damage and covers other rain teams, specifically by taking on the therians. Even though I don't run scald on jelli for the sake of Jirachi spreading and haxxing with paralysis I do run it on rotom because he's immune to the ground types which Jirachi can't paralyse, and burning Chomp or Lando is very important to me. pain split allows me to deal and damage and recover giving him better longevity and synergising well with his low hp.
Salamence @ choice scarf
moxie
hasty nature
252atk/4spatk/252spe
-dragon claw
-outrage
-earthquake
-fire blast
Salamence cleans up Jirachi's mess with ease. Most faster scarfers end up either paralysed, paralysed and confused or even outright dead when he hits the scene. The only things he really has trouble with are Thundurus-T and ScarfChomp. Even Ferro is 2hko'd by outrage at +0 when under half. Despite being in the rain Fire blast OKHOs standard genesect after two rounds of rocks or one round of rocks and Ferro's iron barbs if he u-turns on him. Moxie allows him to be both a late game sweeper and a mid-game revenge killer because he only needs one move to sweep, therefore the scarf isn't a hindrance. because he only really switches in once or twice a match and ideally sand storm won't be present rapid spinning can be forgotten. mence's greatest enemy is residual damage and priority, because he'll be coming in at the end to clean up there isn't a lot of opportunity to stop him. Choice Band Scizor's bullet punch deosn't OHKO even after rocks and he resists both aqua jet and mach punch. Mamoswine is a problem but he can be worked around with the rest of the team, especially rotom's burn support.
All rates are appreciated.
Jirachi @ Leftovers
Serene Grace
Quiet nature
252hp/252spatk/4spdef
-thunder
-iron head
-water pulse
-substitute
This Jirachi is a total ass under rain, on top of having enough hp for his sub to survive seismic toss and losing his fire weakness he has a 120 bp move with a 60% paralysis chance, a pseudo stab on water pulse which has a 40% chance of confusion and of course iron head is a decent stab with a 60% chance to flinch. He gets a sub up ridiculously easily because of his great bulk and steel typing. Assuming he gets a paralysis with his thunder which he's likely to do the opponent only has a 75% chance to move. If he's confused he only has a 75% chance to move divided by 2, and if I'm using iron head take that and subtract 60%. It only gets worse if they're using a less than 100% accurate move and/or can't break my sub with 1 attack. His attacks also have decent synergy with each other and special attack investment means I deal decent damage while haxing the opponent.
Politoed @ choice specs
drizzle
modest nature
252hp/252spatk/4spdef
-hydropump
-focublast
-hidden power [grass]
-ice beam
Politoed brings the rain and provides some immediate power to the team, he does a good job forcing out all the other weather starters assuming he comes in on them and can nail 3 of the 4 with a super effective coverage move as they come in. Hidden power grass mess up water grounds like gastrodon as well as lanturn who mess Jirachi's shenanigans up. He also does decent damage to Ferrothorn who also walls Jirachi, especially since iron barbs hurts more than iron head. he also just barely survives standard genesect's thunderbolt even at +1 and KOs back with hydropump.
ferrothorn @ leftovers
iron barbs
sassy nature
252hp/88def/168spdef
-power whip
-stealth rocks
-leech seed
-protect
Ferrothorn is a boss, no questions asked. I added him to better take dragon attacks because of his wonderful mixed defences. I run leech seed for the passive damage and recovery and protect to exploit it, the one extra turn can often make the difference in a match and the nice little boost from seeds gives me a bit of leeway for his replacement when he switches out. I elected to run only stealth rocks because I would rather be able to set up quickly and it's better if for me because they hit every pokemon not just grounded ones. I also didn't have to be very centred on my spin blocking because it's easy to set them up again and again. Power whip has slightly better coverage than gyro ball and gives me an additional way to break bulky waters.
Jellicent @ leftovers
water absorb
calm nature
252hp/36spatk/220spdef
-surf
-shadow ball
-ice beam
-recover
Jellicent joins with Ferrothorn to create the famed ferrocent defensive core of hazard laying and spin blocking, resisting 15 of the 17 types together. because Jirachi excels with paralysis support a status spreading Jelli would clash with that, instead I run a 3 attacks + recover bulky attacking tank. Surf and shadow ball are stabs while ice beam is simply a phenomenal attacking type in general and pairs nicely with water to hit the grass types that resist it. Jelli's also great at tanking special attacks and provides a useful fighting immunity.

Rotom-Wash @ leftovers
pressure
modest nature
184Hp/4def/144Sp/176Spe
-hydro pump
-volt switch
-pain split
will-o-wisp
Rotom-Wash pairs with FerroCent quite nicely, resisting flying and being immune to ground- the two types that hit Ferrothorn and Jellicent both neutrally make it a great partner. It does sadly give this team a third grass weakness however with 3 resists, two of them being double resists it's nothing that can't be dealt with with smart switching. Rotom also provide utility in volt switch however he has no u-turner to join with. He does decent damage and covers other rain teams, specifically by taking on the therians. Even though I don't run scald on jelli for the sake of Jirachi spreading and haxxing with paralysis I do run it on rotom because he's immune to the ground types which Jirachi can't paralyse, and burning Chomp or Lando is very important to me. pain split allows me to deal and damage and recover giving him better longevity and synergising well with his low hp.

Salamence @ choice scarf
moxie
hasty nature
252atk/4spatk/252spe
-dragon claw
-outrage
-earthquake
-fire blast
Salamence cleans up Jirachi's mess with ease. Most faster scarfers end up either paralysed, paralysed and confused or even outright dead when he hits the scene. The only things he really has trouble with are Thundurus-T and ScarfChomp. Even Ferro is 2hko'd by outrage at +0 when under half. Despite being in the rain Fire blast OKHOs standard genesect after two rounds of rocks or one round of rocks and Ferro's iron barbs if he u-turns on him. Moxie allows him to be both a late game sweeper and a mid-game revenge killer because he only needs one move to sweep, therefore the scarf isn't a hindrance. because he only really switches in once or twice a match and ideally sand storm won't be present rapid spinning can be forgotten. mence's greatest enemy is residual damage and priority, because he'll be coming in at the end to clean up there isn't a lot of opportunity to stop him. Choice Band Scizor's bullet punch deosn't OHKO even after rocks and he resists both aqua jet and mach punch. Mamoswine is a problem but he can be worked around with the rest of the team, especially rotom's burn support.
All rates are appreciated.