>>381536351, but as an end-game common, something you'd find in Victory Road. The base stats are fine for something mid-game but if Melmetal isn't nerfed there's no way it can be in the earlier parts of the game without ruining it like how Riolu is in XY. Also I suspect that unless other Anons are correct about it being a Magnetic Area Evo, Meltan will evolve at Level 40.
If you were to nerf Melmetal's stats to a more acceptable range they'd be;
HPP: 135 -(-22)-> 113
ATK: 143 -(-24)-> 119
DEF: 143 -(-24)-> 119
SAT: 80 -(-13)-> 67
SDE: 65 -(-11)-> 54
SPD: 34 -(-6)-> 28
BST: 600 -(-100)-> 500
If you wanna add a mega that boosts Melmetal back up to its original stats that's fine but it wouldn't be good for SS if such a powerful Pokemon could be so easily obtained especially early on.