Suggested by Sonic Jirachi may have the power of wishes on his side but that’s not going to be enough to stop a powerful demon like Demigra. Demigra’s powers are on a completely different level and his energy attacks could beat Jirachi in a single move. It’ll be difficult for the Pokemon to be able to keep up at all before being blown away. Demigra wins.
Jirachi is definitely not one of the strongest pokemon around, but at least he has wish powers. A lot of good that will do him. Ness will beat him with his PK powers. Ness has fire and green energy attacks. Ness wins.
Update! I think that Jirachi’s array of powerful pokemon attacks will get the job done in this round. Nothing can stop a well planned Hyper beam and his speed isn’t that bad either. Jirachi wins.