Jirachi (the Wish Pokémon) is a legendary Steel/Psychic-type Pokémon found all across the planet, though their population numbers are exceptionally low. Regarded as tiny miracles for their ability to grant wishes, Jirachi are truly unique creatures that are still relatively mysterious in regards to the function of their abilities. Even so, you certainly shouldn't give up the chance to make a wish if you're ever lucky enough to find one of these creatures; after all, they only wake up every thousand years or so, so it's unlikely that you will ever get the chance to make your wish come true ever again!
Jirachi are amazing creatures that literally defy the boundaries of science with their tremendous psychic abilities, particularly because they are all geared toward doing one thing only: granting wishes. No one is exactly sure why Jirachi live for this one purpose only nor is there any clue as to their origins, but it is obvious that it takes a considerable toll on the creatures as they only ever awaken once every thousand years or so. Despite what some may think, Jirachi are able to grant wishes of literally any kind, ranging from the material (which can be done through simple teleportation) to the completely non-material (such as wishing for good luck in the family for the next thousand years, something that has been completely confirmed in at least one case); this intense degree of psychic control puts a tremendous strain on the brains of Jirachi, forcing them to take extensive time to fully regenerate their powers and allowing them to only remain awake for seven days at a time. When not awake, Jirachi protect themselves in a cocoon of quartz infused with high amounts of psychic energy, granting them invincibility against everything short of magma-producing temperatures. Even if they are asleep, though, Jirachi can still fight back with tremendous force and deal considerable damage to intruders despite the fact that they are unable to use their full power. Thankfully for humans, whose lives are rather short, it is said that a voice of pure innocence can wake up a Jirachi for at least a few minutes, giving them enough time to make a wish; failing that, if a human notices that a Jirachi has shed its crystalline cocoon (which happens once they are about 10-100 years away from awakening again), they can simply write their wish on the streamer-like growths attached to their heads. This is effective because Jirachi will actually grant any wishes that have been placed on them as a memento to those who otherwise would have missed the chance to make their wishes come true, showing that these creatures demonstrate exceptional sentiment towards humans for some odd reason. It is lastly noted that, if placed in an intense combat situation, Jirachi can call upon their own wish-granting powers to generate a massive energy blast that, like a wish, takes a little time before it is fully granted; once it does hit, however, the damage can be catastrophic because of its special attributes. This unique special attack, known as the Doom Desire attack, is technically considered to be a Steel-type attack because of its unique reliance on light without heat to deal damage, and although it takes about as long as a Future Sight attack to work, the sheer damage it is capable of more than makes it a move worth fearing in battle.
While Jirachi are usually kept hidden away from the public eye, there is one recent event involving a Jirachi that should be taken note of, namely the Millennium Comet Incident. A Jirachi located within a haven of nature in the Hoenn region, known by the locals as Forina, awoke every thousand years in correlation with a rare comet, known also by the locals as the Millennium Comet, and absorbed the energy within the comet in order to expel it out upon the life forms within Forina in order to grant the local flora the strength needed to grow and stay healthy through many generations despite the otherwise harsh conditions of their local environment. A few years ago, however, during the comet's last sighting, a former member of Team Magma known as Butler attempted to use Jirachi to do what no one had ever done before: resurrect the 'believed-to-be-long-gone' legendary Pokémon Groudon. He had a fossilized piece of Groudon hide and had attempted to resurrect it many years prior with technology alone but, in failing to do so, was kicked out of Team Magma. Frustrated, Butler went so far as to steal Jirachi from a group of local kids who had discovered it and had been there when it had awakened, forcing it to use its full-wishing-granting powers to directly absorb the energy of the Millennium Comet and use it to grant Butler's wish (the resurrection of Groudon). Unfortunately, as we now know, Groudon was not extinct and is still very much alive today, so Butler's wish was flawed; the result was the creation of a being that reflected not Groudon but Butler himself, effectively a giant fake Groudon that wanted only to suck the life out of everything it touched simply because it could. Butler realized his mistake too late and would have been the cause of many lost lives if it had not been for the courageous efforts of the children who discovered the Jirachi; through their efforts, they were able to free and revitalize Jirachi, giving it enough power to destroy and effectively re-absorb the monstrous fake Groudon with a super-powered Doom Desire attack. After the incident, the Jirachi involved went back to sleep in Forina, and Butler is presumed to have moved on to a better life in a different region.
Though their psychic powers may still be bordering the definition of impossible in some cases, it is undoubtedly certain that Jirachi are wonderful creatures that likely have a lot yet to tell to the scientific community. Despite the fact that they may be steeped in as much lore as Ghost-types and present little in the way of understandable fact, one can't help but feel glad to know that miracles, even if they are only small ones, are still possible. If you ever get to see one of these creatures awaken before you die, though, make sure that you understand the consequences of your wish before you make it; after all, they might be able to do just about anything, but that doesn't mean that the average person should ignore the story of the Monkey's Paw, lest you find yourself locked into a nightmare only a thousand years can cure!