Whyvern King is a Yo-kai with clay-colored skin, pointy ears and purple eyes. He has long red hair that spreads around like wings and two large horns that jut from his forehead. Whyvern King also has a large crimson colored dragon tail with a tuft of yellow fur at the end of it. A necklace hangs on his neck with different sized crystal orbs. A white robe goes over Whyvern King's shoulder with purple stitches tied to a purple sash. Under the robe, Whyvern King wears a teal colored kimono and a navy blue hakama.
Whyvern King appears as a Legendary Yo-kai starting from Yo-kai Watch 3. As a Legendary Yo-kai, one must befriend and/or recruit the following Yo-kai first in order to undo his seal.
Befriended: Why did I lose, and why are you so strong? Also, why not be my friend?
Loafing: What was that?
Traded: Wh-why did I get traded away? And why are you staring at me like that? Why?!
Nandaryuuou is named for "Nandaryūō" (Japanese: 難陀竜王,"Nandaryūō"), also known as Ānanda. His Medallium bio also suggests a connection to the phrase "nanda?" (Japanese: "何だ?","What's this?")
"Whyvern King" is a combination of "why," "wyvern," and "king."
König Whyrum is a wordplay of "König" (king) "Wyvern" and Warum ("Why")
As his name suggests, he is based on the dragon king of the same name, one of eight Dragon Kings as mentioned by the Lotus Sutra.
Unlike Princess Pearl and Asura, only one of the Yo-kai needed to unlock Whyvern King is not exclusive to the version that he is available in. In this case, Dragon Lord is not exclusive to Yo-kai Watch 3: Sukiyaki.