Pokémon Mystery Dungeon: Blue Rescue Team and Red Rescue Team/Buried Relic

After beating Stormy Sea, you should receive mail about the Buried Relic. Go to Pokémon square and talk to Lombre then Shiftry to unlock this massive dungeon.

Note: do not enter the dungeon until you buy the friend area Final Island.

The Dungeon
Warning: This dungeon requires a quicksave before entry, so don't take anything important with you.

The first fourteen floors shouldn't be too hard. You'll face Regirock on the 15th, Regice on the 25th and Registeel on the 35th. Each will drop a part. When you have all three parts, they will fuse to become a music box. From floor 36-98, there is a chance of encountering Mew as long as you possess the music box. Do not try to use it, if you do the music box will break! You can recruit him if you have the Final Island friend area. There are only Golem on floor 99.

There is a chance of finding buried items and Monster Houses on any floor.

Special Items
WARNING: If you befriend Mew, some chances are that you can't get these items, so if you want the items come back to the dungeon without fainting
 * HM Rock Smash on floor 45 if you have a key
 * HM Strength on floor 60 if you have a ghost Pokémon or a Pokémon that knows rock smash
 * HM Flash on floor 70 if you have a key
 * HM Cut on floor 80 if you have a key and a water Pokémon
 * Rock Part Gained by defeating Regirock
 * Ice Part Gained by defeating Regice
 * Steel Part Gained by defeating Registeel
 * Music Box Once all 3 parts are collected they will become this

Enemies
If you befriend Mew you will be instantly teleported out of the dungeon.