One day I was checking nearby pokemon, and suddenly found all 5 gyms around me had a Melmetal standing on top. Is it really good for gym defense or just showing off? I thought they used hundreds of rare candies to evolve and power up (or walking for nearly 10000 kms O_O).
You can get 19 meltan catches (6 candy per with Pinaps, then trade/transfer for more) per week by connecting to Pokemon Go.
So it doesn't require rare candy - people are probably getting enough of the candy now to finally have some good ones (not to mention opening the box in snow to catch wild boosted Meltan up to level 35 makes them gym-ready quickly).
Melmetal is okay, but it isn't amazing. It's weak to two quite common types in Fire and Fighting. (And shares a weakness with the fat normals) However, it has pretty good counter coverage.
But there's a problem, you need two charge moves for it to be viable, which are Flash Cannon and Rock Slide. Flash Cannon covers the dual typed Ground attackers (Rhyperior, Rhydon, Mamoswine) and also may knock out a Machamp before it goes down. Rock Slide is pretty self explanatory, absolutely maiming Moltres and Charizard.
That alone costs 100k stardust and 100 Meltan candy, which may not be easy for those who didn't buy the console and the game. (And don't forget it costs 400 candy to evolve in the first place)
