What Do You Do With the Mysterious Machine in 'Pokemon Emerald'?by Joshua Phillips ; Updated September 22, 2017
"Pokemon Emerald" combines the stories of both "Pokemon Ruby" and "Pokemon Sapphire" but with a few subtle changes. Halfway through the game, the nefarious Team Magma uses a meteorite to power a mysterious machine deep within Mt. Chimney in an attempt to make it erupt and expand the landmass of the world.
Reaching the Mysterious Machine
After obtaining the third gym badge from Wattson, the gym leader of Mauville City, you travel to Fallarbor Town. Fallarbor Town is located north of Mauville City, requiring you to travel through Routes 111 and 113. Exit Fallarbor via the western exit until you reach Team Magma and Team Aqua fighting with each other over the meteorite. Once the fight is over, the cable car on Route 112 is now active. Return to Route 112, located to the left of Route 111 before Route 113, and use the cable car to reach Mt. Chimney. Travel north through Mt. Chimney until you reach Maxie, the leader of Team Magma, who is guarding the mysterious machine behind him. Save your game before approaching him, as he challenges you to a fight.
Maxie uses three Pokemon: Mightyena, a Level 25 Dark-type, Golbat, a Level 25 Posion- and Flying-type, and Camerupt, a Level 28 Fire- and Ground-type. Defeating his Pokemon requires Pokemon around the same level that are the opposite type. For Mightyena, use a Fight- or Bug-type Pokemon. For Golbat, use an Electric-type Pokemon. For Camerupt, use any Water-type, as it's effective against both Fire- and Ground-type Pokemon, of which Camerupt is both. Throughout the fight, Maxie uses items to restore the health of his Pokemon when it falls below 50 percent. However, he uses only one health item per Pokemon. Use your own health-replenishing items if your Pokemon's health falls below 50 percent.
Retrieving the Meteorite
Once Maxie is defeated, he escapes as the leader of Team Aqua appears. However, the leader of Team Aqua doesn't fight you, instead thanking you for defeating his rival. After Archie leaves, you can now interact with the mysterious machine -- the small grey box on the edge of the lava behind Maxie's original position. However, the only interaction you can have with it is taking the meteorite out of it. Stand next to the machine and press "A." Select "Yes" when you're asked if you want to remove the meteorite. The text "(Your Player Name) removed the meteorite from the mysterious machine" appears. The meteorite is then placed into the "Key Items" section of your bag. After the meteorite is removed, the mysterious machine has no more use.
Reward for the Meteorite
The meteorite's only use is to be exchanged for a reward; it can't be sold and can only be given to one person: Professor Cozmo. Leave Mt. Chimney and return to Fallarbor town. Professor Cozmo's house is located on the southern section of town to the right of a large crater. Speak to Cozmo inside of his house; when he asks for the meteorite, give it to him. To thank you for the Meteorite, Cozmo gives you TM27, Return. This move does additional damage to a Pokemon if the Pokemon using it has a high happiness rating.