To catch Meltan in Pokemon GO, you must open the Mystery Box item, which is obtained after sending Pokemon from Pokemon GO to Pokemon HOME or Pokemon Let’s GO Pikachu/Eevee.
Once you open the Mystery Box, one Meltan will spawn every 90 seconds for 30 minutes.
Here’s how to send Pokemon from Pokemon GO to Pokemon Home and Pokemon Let’s GO: Pikachu/Eevee. The process can be difficult to set up, but it is definitely worth it as you must transfer a Pokemon every time you use to Mystery Box!
Additionally, players can sometimes get a Meltan reward encounter for completing specific Research in Pokemon GO. For instance, completing the Pokemon GO Let’s GO Collection Challenge gives a Meltan encounter.
What’s more, the Willow’s Wardrobe Timed Research includes a guaranteed encounter with Melmetal! This is the evolved version of Meltan.

How to Get Mystery Box in Pokemon GO
To get the Mystery Box in Pokemon GO, you must transfer a Pokemon from Pokemon GO to either Pokemon HOME or Pokemon Let’s GO: Pikachu/Eevee.
The first time you do this, you will receive the Mystery Box. Every time you use the Mystery Box again, you must transfer another Pokemon to HOME or Let’s GO: Pikachu/Eevee.

What Does the Mystery Box Do in Pokemon GO?
Opening the Mystery Box in Pokemon GO causes Meltan to spawn in the wild for 30 minutes. One Meltan appears every 90 seconds.
To open it, you must first activate The Mystery Box by sending a Pokemon to Pokemon HOME or Pokemon Let’s GO: Pikachu/Eevee.
In addition to causing Meltan to spawn, the box can also spawn shiny Meltan during some Pokemon GO events!

How Often Can You Use the Mystery Box?
You can use the Mystery Box in Pokemon GO once per week.
However, some in-game events, like the Pokemon GO Let’s GO event have bonuses that increase how often you can use the Mystery Box. This allows you to catch more Meltan and earn more Meltan Candy.

Now that you know how to catch Meltan, you’ll have one more Mythical Pokemon in your Pokedex. Find out how to catch every Mythical Pokemon in Pokemon GO, so you don’t miss any!