There is one way.
You have to recruit every single non-legendary Pokemon in the game other than Kecleon. You have to be Lucario Rank. Then you have to clear Wish Cave, while holding the Wish Stone, refuse Jirachi's offer to join the team, and wish for "something good".
If you ask me, I'd rather bring two Petrify Orbs and a teammate with Helping Hand, and save scum to victory.
You have to recruit every single non-legendary Pokemon in the game other than Kecleon. You have to be Lucario Rank. Then you have to clear Wish Cave, while holding the Wish Stone, refuse Jirachi's offer to join the team, and wish for "something good".
If you ask me, I'd rather bring two Petrify Orbs and a teammate with Helping Hand, and save scum to victory.
...Is there even any other way of recruiting these?