Bubbul Gem

are NaN Items in.

Location and Uses
NaN Bubbul Gems are dropped by NaN Bubbulfrogs, found in the caves scattered throughout Hyrule, when defeated. They can then be traded to Koltin for monster parts and gear.

The first trade is part of the "The Hunt for Bubbul Gems!" side adventure which can be started by interacting with Koltin outside the Pico Pond Cave in the Eldin region. Link will be tasked with entering the cave and retrieving the Bubbul Gem from the Bubbulfrog inside. Upon speaking with Koltin, he will trade Link the Bokoblin Mask in exchange for the Bubbul Gem he collected.

After completing the quest, Koltin can be found in various locations across Hyrule where he will make the following trades:

Once Link has traded 46 Bubbul Gems to Koltin and obtained the Mystic Headpiece, Koltin will ask Link to find the remaining Bubbul Gems even though he has no rewards left to give him. If Link collects the remaining gems and gives them to Koltin, he will give Link the Koltin's Fabric, asking Link to show it to his brother Kilton. Koltin then transforms into a Blupee and disappears.