Once a Kupo Nut has been acquired, attempt to cross the river in Gloombell Forest. A cutscene will start that introduces Mooglenyan. Mooglenyan will then proceed to tell the player that he can't find his friends.
Talk to Mooglenyan and start the quest "Fantastic Find!"
Search around Gloombell Forest to find all five missing Mooglenyans. Rotate the camera with the L and R buttons to help the player find them.
The first missing Mooglenyan can be found next to the tree south of where the player starts the quest.
The second missing Mooglenyan can be found in the northeast corner of Gloombell Forest near the Eyepo.
The third missing Mooglenyan can be found in the northwest corner of Gloombell Forest.
The fourth missing Mooglenyan is near the swing set and the rocks. He is looking at a teddy bear.
The fifth missing Mooglenyan is in a crib south of Rocky Badboya.
After finding all five missing Mooglenyans, talk to the Mooglenyan with the quest icon over his head. Upon talking to him, Mooglenyan will give the player his Yo-kai Medal, and the quest will be completed.
During the Mooglenyan Slingshot Battle event, the player could get Kupo Nuts. Using the Kupo Nut will take the player to a map called Fantasy Forest. The map contains a single stage with Mooglenyan. The player has to beat Mooglenyan on this stage for a chance to befriend him.
During the Dissidia Final Fantasy NT Collaboration event, Mooglenyan can be fought on Hidden Stage One on the second event map. During this event, the player would unlock Hidden Stage One by beating Stage 21 with Chocobonyan's Soultimate.