burned relic

(It is called Buried Relic)
After clearing the Stormy Sea, you will receive a new mail about the Buried Relic in your mail box. Go to the Pokemon Square, talk to Lombre and Shiftry and they will grant you access to the Buried Relic.

NOTES: Compulsary save before entry. After collecting all three RockParts, IceParts, and SteelParts from the Regis, the Orgel will be constructed. Mew will appear randomly when item is in bag. You will be automatically transported out of the dungeon if successfully befriended Mew.

You have to recruit Kyogre in Stormy Sea, to get, talk to Medicham near team base twice I think, then speak with Lombre, then Whiscash. He will give you HM Dive to go to Stormy Sea. Once you recruit Kyogre, the next day you will see a newsletter that talks about the Buried Relic, talk to everyone in Pokemon Square, then go to Buried Relic. You have to save before entering, this means that if you faint, you cannot turn off the game and end up in your team base, like if nothing happen. If you turn the game off, you will lose all your items and money, just like a quick save.ONce you beat all the Regis (15F, 25F, 35F) you can collect the item they all leave behind, and once you have all three, a music box will be formed. The box will allow Mew to appear, but he only appears in Monster Houses and the 1st room you enter.
From: Alexx