Grainpa in Yo-kai Watch 1

Grainpa is in a normally inaccessible area of Hungry Pass past the S rank Watch Lock in the Yo-kai World, where he can be challenged once a day until he's befriended through normal methods. He is, despite being a Rank B Yo-kai, a very strong opponent, and a team of around level 60 is recommended to fight him

He can also be encountered in the back alley near Timers & More in a Yo-kai Spot.