Chummer appears in the Springdale Underground Waterway. The easiest way to reach the area they are located if you've never been to the Springdale Underground Waterway before is to enter through the drainage pipe located on the western side of Uptown Springdale just near the canal.
Chummer can be found at the Hidden Workshop in San Fantastico.
Befriended (Yo-Kai Watch): "Of all the chum I've chomped on, you're the chummiest!"
Befriended (Yo-kai Watch 2): "Of all the chum I've chomped on, you're the chummiest!"
Receiving food (favourite): "Really good!"
Receiving food (normal): "Huh..."
Receiving food (disliked): "Why me?!"
Freed from Crank-a-kai: "Free at last! Wanna be...chums?"
Chummer was first summoned in the 1st movie as part of Nathaniel's team.
Ironically, despite being depicted as an omnivorous Yo-kai, because Chummer's favorite foods are Vegetables in the games, he hates meat.
"Michikusame" is a portmanteau of michikusa ("loitering, fooling around", literally written as "roadside grass" as grassy roadsides are the archetypal spot for that sort of activity) and same ("shark").
"Chummer" is based on the word chum, which can mean "friend" or refer to a mixture of fish guts and blood, which is then scattered over water to attract sharks in a practice known as "chumming".