Here is the answer in case anyone needs it as written on the wiki
Yo Kai watch 2
Use a travelers coin available by a password
Or for Yo Kai watch 3
Grumpus Khan can rarely be found under vending machines in Uptown Springdale.
He may also appear in battle during the seasonal Rare Yo-kai course in Ambrosia Pavilion.
Finally, he can be freed from the Crank-a-kai using a Dark Blue Coin
