A mystery part is obtained through a wondermail mission. Here is a wondermail code for a mystery part which i got.
S4YS 43PX N8H3
9W4+ @%Q- 7XM-
You need quicksand cave for this.
First you need a mystery part or enigma part. Then go to mystery jungle at BF13. Celebi will be there.
Get a Secret Slab or Mystery Part, and go to Surrounded Sea B18F. Lugia's there, but ONLY with the Secret Slab or Mystery Part. but i went there twice and it was only there the first time
you get celebi in time & mewtwo in darkness but the only way you can get them is by having the secret slab or mystery part
you do a misson with umberon
you can find him in midnight forest fl. 24 if you have mystery part OR secret slab
technically yes, but you need a mystery part to be able to
shimmer hill 18f you need mystery part and or secret slab
You can get them from random missions.
Mt. Mistral 18th or 19h floor with the mystery part or secret slab in your bag
Well there is no true mystery part in the name "Mystery Dungeon", but I guess you could say the mystery is what you will encounter in the dungeon.
maybe you can get the secret slab and mystery part in your treasure bag
I used the Wondermail Generator online to obtain it.