The addition of the Sumeru region also marks the debut of playable Dendro characters in Genshin Impact. As is the case with a character of every other element, Dendro characters utilize specific materials for Ascension that are exclusive to them. One such material is Nagadus Emerald Chunk, a rare resource that can only be found in one location.
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Unfortunately, you cannot find Nagadus Emerald Chunk in the open, and it can only be obtained by defeating Jadeplume Terrorshroom or crafting. That said, this could also be a blessing in disguise as you don't have to go on a long search for the resource, which could be time-consuming.
You will be able to find Jadeplume Terrorshroom in the extreme northwest of Sumeru, but you won't be able to walk to the world boss simply. In order to reach Jadeplume Terrorshroom, you must first unlock the nearby Statue of The Seven. Once the statue is unlocked, go near the Jadeplume Terrorshroom's location and look for a portal. This is because, despite the location of the Jadeplume Terrorshroom being marked on the map, you won't be able to reach the boss as it is hidden underground. There is a portal nearby the Jadeplume Terrorshroom's location, which, once used, will automatically lead you to the boss. Defeating the boss will net you several rewards, including Nagadus Emerald Chunks.
Another way of obtaining Nagadus Emerald Chunks is through crafting. By using 3x Nagadus Emerald Fragment and spending 900 Mora, you'll get a single Nagadus Emerald Chunk. While crafting won't usually suffice the amount needed to Ascend characters, it can come in handy if you are short just by a few.