Giant Volcano is a dungeon in Explorers of Time/Darkness and Sky. It can be unlocked by using a Wonder Mail Code. The Pokemon (except for Moltres and Heatran) can also be found in Dark Crater (except for Mewtwo only in Darkness version). In Explorers of Sky in 10F, Moltres is there if you have the Mystery Part or Secret Slab. At the summit there is Heatran waiting for you. After you defeat him, you get the Fiery Drum. There is also a chance that he will join your team after you defeat him.