The Metagrossite quest is the questline done in order to acquire the Mega stone for Metagross—the Metagrossite.
To make the quest go as smoothly as possible, these preparations should be made:
- A full team of Steel type Pokémon
Starting the quest
To begin the quest, you must head to Mossdeep City and find Steven's house, which is on the right side of the island, just below the Space Center. He tells you that he's been hearing a lot about you recently and notices you have a Mega Bracelet. Along with some scientists, Steven is trying to replicate a Metagrossite, but they need some help. He will then ask you if you are willing to help them out, to which you should accept and begin the quest.
Replicating the Mega stone
Steven explains that Metagross is simply the combination of two Metang and that the fusion of the two Metang will serve as the foundation for the Metagrossite replication. But, Metang are rare, so they have none to fuse with. Your first mission is to give Steven 2 Metang with 100 or more IVs each.
They do not need to be your OT, but they do have to be caught after speaking with Steven. They will be permanently deleted, so think carefully about the Metang you give him.
Once you have given Steven the Metang, he will begin the fusion process. He predicts the fused Metagross will be hungry and angry. Thus, he requests that you bring him 3 Pokémon with 70 or less IVs that the Metagross can consume to calm down. These 3 Pokémon is that they can be any type, except Steel and must be caught after speaking with Steven.
After giving the 3 Pokémon, Steven will be able to successfully replicate the Metagrossite. He will then test the stone's effects on a Metagross he has. The replicated Metagrossite works but the Mega Metagross is unhappy and attacks Steven. You must now defeat the Mega Metagross before it causes more damage. You can only use Steel type Pokémon for this battle. Once you are ready, speak with the Mega Metagross to initiate the battle.
Following the defeat of the Mega Metagross, Steven will thank you for saving him and any potential damages the Metagross may have caused if you hadn't stopped it. As a reward for all your help, he will gift you the Metagrossite.