They live in mountains where no trace of humans can be detected. Jangmo-o grow little by little as they battle one another.
– Pokémon Moon Pokédex
Jangmo-o was apparently the first gen 7 Pokemon to be designed. It appeared in the Sun/Moon demo for a trial that was not in the main game.
If you want a Razor Claw for evolving Sneasel, fighting wild Jangmo-o is the only way to acquire the item in Sun/Moon. Wild Jangmo-o have a 5% chance of holding a Razor Claw.
It only learns Normal and Dragon type damaging moves by level-up, which means it cannot hit Mimikyu, who is immune to both types.
Stat-wise, it has pretty even stats, with 45 in HP, Sp Atk, Sp Def, and Speed. It has 65 Def and 55 Attack.