If you want to get Meltan in Pokemon GO, you need to have a copy of Pokemon Let's Go and a Switch, or you need access to a Mystery Box. This is why Pokemon GO players without the necessary software/hardware have been working with Let's Go players to receive Mystery Boxes that grant Meltan. It's always nice to see the community working together, but a group of players in Singapore took their collaboration got a completely new level.
An event in Singapore aimed to give Pokemon GO players without a Switch/Let's Go access to Meltan. Those players could get a Mystery Box if they brought food to donate to a charity. Believe it or not, 118 different players gathered and donated food in order to get Meltan. This is such a fantastic idea that I wouldn't be surprised to see other places hopping on it soon!