Reposting from the Stark version of this thread. This was a set I designed almost a year ago for use in the CAP metagame (Cyclohm was the most recent CAP creation). It did very well back then, but now it runs into problems with Colossoil, and I haven't used it since CAP9. However, cyberzero reports that he still functions very well. :)
108 hp / 224 SpA / 176 Speed
~Psychic / Flash Cannon
This set abuses Jirachi's unpredictability to the fullest extent. The idea of this set is that it can switch in and out pretty easily to feign a bizarre Choice set, and he can start Calm Minding at any point. Once your opponent sees Calm Mind, you can bet that Blissey will be switching in in a second. Most will expect a Substitute and won't even try to Thunder Wave Jirachi. By slapping Blissey with a Toxic Orb, you fully incapacitate her for the remainder of the battle. Psychic + Thunderbolt, which I've been using, also tends to lure in Celebi, another excellent Toxic Orb victim.
The amount of Pokemon that hate a Toxic Orb is almost absurd, but the primary Pokemon to aim for are Natural Cure pokemon, Rest/Talk users, and sweepers who take a long time to set up, like Sub/Charge beam Rotom-a. While the general goal is to take out a Blissey, your opponent will often end up not having one, so it's good to know that this Jirachi will not go to waste.
If you get lucky, and you've Tricked a Blissey or Celebi that hasn't got Thunder Wave or Flamethrower/HP-Fire, this Jirachi can often make breakaway sweeps right out of the middlegame. Jirachi's counter can't stay in for long when he's accumulating Toxic damage and without Leftovers, and Jirachi has no trouble KOing the majority of OU Pokemon after a couple of boosts.
I assume Flash Cannon can be used over Psychic, though I haven't tested it. It may be better in the current CAP metagame with Colossoil running about. Thunderbolt + Flash Cannon Jirachi is normally walled by Swampert, but I'm certain that Swampert will just love a Toxic Orb.
176 Speed EVs with Timid beats all Lucario and everything slower. Again, in the current metagame I would probably just run maximum Speed (but this is totally untested). 108 returns exactly 368 HP, which is meaningful for two reasons: it is divisible by 16 with one remainder, meaning that a stolen Leftovers will heal one more point per turn than they would with 104 EVs, and a stolen Life Orb will damage you one point less than it would with 116 EVs. No HP EVs is fine, but I like my Jirachi with a little bulk. I used to run max HP, but I decided I like to boost the Special Attack.
An interesting twist on this set is to use a mixed Jirachi with a Naive nature and a moveset like Iron Head / Fire Punch / Thunderbolt / Trick. Iron Head is for typical Jirachi dickery and Fire Punch keeps those pesky toxic-immune Steels away. With that set, one would intend specifically to feign a Choice Scarf and lure in different threats. While less bulky and less powerful, it fares considerably better against Tyranitar and Scizor.
Obviously, this set functions best in the best environment. As it tends to clear out special walls, it functions extremely well alongside special sweepers. I'm using a ScarfTran, a Calm Mind Latias, and a SubPetaya Empoleon alongside this Jirachi, and it's very rare that I won't be able to clean up with one of them. In the CAP metagame, my team was somewhat different; it featured a Stratagem.
The reason why I used this set over the more common Toxic Spikes is because back in autumn of 2009, every team on the CAP ladder had a Fidgit. If I wanted to poison Blissey & co. permanently, I had to use a Dugtrio with Toxic Spikes, or use a Trick Toxic Orb lure. Where Toxic Spikes takes two turns to set up, requires you to use sometimes awkward Pokemon like Roserade or Tentacruel, and is highly vulnerable to Rapid Spin (and occasionally Aromatherapy), this Jirachi is simply a one-time lure who can put an end to a Pokemon that gets in your way.
Originally Posted by Fat Rising_Dusk
This set must be used in a sandstorm
or it is poor.
So why not use Weather Ball for a stronger STAB?