¡Buu, ja, ja!

You'll need to find the little ghost 4 times inside the Fyxestroll Gardens, the quest chain is started via the first encounter up the elevator in the lower right corner of the map.

"Ya-ha-ha!" is the sound made by the Koroks, a race of forest people in video game series The Legend of Zelda. The chive's condition is a reference to a quest in BotW: after collecting 900 Korok Seeds, the elder Korok Hetsu will tell Link that all Koroks have returned to the Korok Forest. - Credit: Necrosyrtes