jirachi.
go to silver trench first then get lugia to join your team then meteor cave will be unlocked
20 floors.
19 deoxys is on the the 20 (the real deoxys)
after Befriending Lugia Meteor cave will open up.
meteor cave seems rather a easy dungeon, having only 20 floors and one enemy on each floor only
i believe you have to befriend with lugia
you get it by entering meteor cave, which is found by blastoise the next morning after recruiting lugia
there is 20 hope i helped
When you recruit Lugia in Silver Trench, the next dungeon will be Meteor Cave, which is the place you can recruit Deoxys.
he's in western cave
Mewtwo lives in cryptic cave, you can get Cryptic cave from wigglytuff in the Pokemon square.
Western Cave