there was discussion about this little guy last page, and i wanna just add on to that before it's too absorbed by other discussion points :x
scarf jirachi is such a great utility and role compression pokemon for offensive build. it's capable of checking tornadus-t, weavile, mega zam & regular zam, annoying fairies like clefable & mega gardevoir, and (probably the biggest one) latios & latias. it can whittle down fatter pokemon thanks to iron head's (and / or heart stamp's) 60% flinch chance. it provides "offensive" cleric support (doesn't kill momentum & you die) thanks to healing wish. these are all things that are pretty obvious about jirachi, really. however, they are what make it such an easy pokemon to throw on an offensive build nowadays. torn-t and weavile are super common right now, and a lati switch-in is necessary; having a pokemon that can handle those + fairies + more while also providing cleric support is huge.
however, jirachi isn't perfect. it struggles from the same thing every other choice item user struggles with by being locked into a move. on top of this, jirachi doesn't really have great coverage, so it's pretty easy to wall. misplaying with choice item users in general will give your opponent an edge, but misplaying with a choice user who doesn't really like being locked into any of its moves in most situations allows your opponent to gain so much momentum against you.
both tankchomp and landorus-t are at insanely high usage, and jirachi doesn't appreciate either of them, of course. yes, it can hit them hard with ice punch, but if you mispredict there, your opponent will be able to gain so much momentum (like with a lot of choice item users, but a bit worse), and going for u-turn means taking some residual damage usually.
even in light of those negative points, scarf jirachi is just great right now because of how it patches a bunch of holes in a typical offensive team. there's a cost to it, but it can be easily remedied by the rest of your team.