Since I run a rain team of my own, I absolutely need something to safely come in on Tornadus-T and threaten it out or KO it should it stay in. This comes from the same team my Latias set comes from:
Jirachi @ Leftovers
Trait: Serene Grace
EVs: 252 HP / 4 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Substitute
- Calm Mind
- Thunder
- Flash Cannon / Water Pulse
Basic SubCM Jirachi, so we should know how it works. Come in on a resisted hit, Sub up, and boost up from there. However, it works a little differently against Tornadus-T. Against Tornadus-T, Jirachi should react depending on how much prior damage Tornadus-T has. Should Torn-T be anywhere below 63%, Jirachi should go straight for the Thunder to avoid taking unnecessary damage. Should Torn-T be closer to 75% or higher, Jirachi needs to boost up with Calm Mind before striking it down with Thunder. Either method needed can work as Jirachi is only 3HKOed at best by Hurricane (full hazards needed for even a shot at a 2HKO) while Focus Blast is hard-pressed to 2HKO without at least 1 layer of Spikes.
Aside from being a good check/counter to Specs Tornadus-T, Jirachi is also something of a hybrid sweeper. If you find a chance to setup, your opponent can be in for a world of hurt. If Jirachi gets a Substitute up on a special attacker, Calm Mind up. After 2 boosts, even Tornadus-T will be unable to break Jirachi's Subs with any move, even Specs Focus Blast. Thunder relies on rain and hits stuff like Politoed, Keldeo, and Torn-T extremely hard. Flash Cannon is used over Water Pulse so Jirachi can have a reliable move outside of rain. Upon seeing Thunder, Abomasnow and Tyranitar will likely come in, expecting to halt Jirachi's sweep only to be met by a STAB Flash Cannon.
The EVs maximize Jirachi's HP and Speed since it's a bulky sweeper. However, if avoiding a 2HKO from Specs Torn-T's Hurricane with SR and 3 layers of Spikes is a must, then 40 EVs may be shifted from Speed over to Special Defense. This still allows Jirachi to outspeed positive nature base 95 Speed Pokemon and retains its ability to setup on both Chansey and Blissey with impunity (albeit slowly) since max HP gives Jirachi 101 HP Subs. This is a great set for Jirachi on a rain team that needs a reliable check/counter to Tornadus-T as well as many Dragon types such as Latios, Dragonite, and Haxorus. However, it's advised to have a more dedicated Steel type for the Dragons. Although Jirachi can handle most in a pinch, it's lack of recovery keeps it from being able to switch into them multiple times. For this reason, Ferrothorn is a solid teammate as it can cripple faster Pokemon with Thunder Wave and provides Spikes and SR support to facilitate Jirachi's sweep. It also can use Leech Seed, allowing Jirachi to have some form of recovery. Removing Steel types is important as well, so Keldeo is a strong option here. Not only can it remove Steel types with Secret Sword and/or Hydro Pump, but it also appreciates Jirachi's ability to get rid of Tornadus-T, one of the more reliable stops to Keldeo for offensive rain teams. Speaking of Keldeo, Jirachi greatly appreciates a teammate that can switch into it as well as other strong Water type attackers like Politoed and Rotom-W. Without many CM boosts or a Sub, these water types can hit Jirachi hard with rain boosted Hydro Pumps. Latias can reliably switch into and dispose of these Pokemon with Draco Meteor and Psyshock. Latios can as well, but Latias's superior bulk makes her a bit more fit for taking these high-powered moves for Jirachi. Note that this Jirachi can operate for multiple turns in Sandstorm or Hail should the opponent's Pokemon be something you don't want to risk bringing Politoed in on, thus relieving the stress on Politoed to continually switch in to bring rain back.