sorry for double posting
I tested offensive CM and it's legit; I was very surprised with the results. I just used a Timid + Leftovers build. After having a convo on IRC with jc104, Pocket, and Woodchuck, I tested a few more things and came to this proposed set:
name: Superachi! (Offensive Calm Mind)
move 1: Calm Mind
move 2: Psychic / Flash Cannon
move 3: Grass Knot / Thunderbolt
move 4: Hidden Power Fire / Hidden Power Ground
item: Life Orb / Leftovers
nature: Modest
evs: 4 HP / 252 SpA / 252 Spe
Expert Belt, Shuca Berry, and Timid in AC
Thunderbolt and HP Ground can honestly be lumped into AC but they have merit. HP Ground hits Heatran, and Thunderbolt hits bulky Water-types and has pretty good coverage with it. Psychic is better than Psyshock because it hits stuff like Gliscor (and, well, pretty much everything) way harder. Grass Knot hits bulky Water-types and Hippowdon / Tyranitar. Hidden Power Fire hits Ferrothorn, naturally. Life Orb for more power, Leftovers to get more setup. Life Orb is preferred because Superachi doesn't really need to stick around all that long to sweep. The Speed from Timid is nice, but many of the Pokemon Jirachi can set up on / beat are slower than it, so it's not always needed. Modest makes it much easier to deal with Pokemon such as Gliscor (Modest LO +1 Psychic OHKOes) and Landorus-T. Flash Cannon just hits stuff neutrally and hits Tyranitar particularly hard. For those reasons, it's a decent alternative to Psychic.
How it works:
Well, pretty much what you do is, you get rid of Garchomp / Terrakion / other annoying powerful Pokemon that can kill Jirachi. You get rid of Heatran. Sweep! No, really, it's that easy. For hazards, all you need is Stealth Rock. The biggest advantage is that it only takes 1-2 CMs to sweep. That's so much faster than other CM Jirachi, and it has more immediate power (meaning before any CMs) as well. Furthermore, it can fit well into teams that aren't rain teams, which is good. It is especially good on sand, as it is not damaged by the weather, but weatherless and hail teams can easily find a home for it as well. Thunderbolt + HP Ground variants can fit on rain even (you would run Thunder then, naturally). The ease with which Superachi sweeps makes it well worth a set, in my opinion.
jc104 said it was probably worth a set, Pocket said the same, and Seven Deadly Sins thinks it's definitely worth a set.
Thoughts?
EDIT: heh that's a good idea RaikouLover, sorry, I didn't see your post. I'll slash them in.