The title of the short story「竜王が勝負を仕掛けてきた」translated here as "The Dragon King Made a Challenge" is if I'm not mistaken meant to be another one of this series's endless chapter title Pokemon jokes (endless in the WN version anyway, since all the chapter titles vanished in the LN), as it's the exact phrasing used for every Trainer battle challenge in the Japanese version.
To try to preserve the joke's existence it might be worth adapting it to one of the translation choices used in the official Pokemon game translations like "The Dragon King Wants to Fight", "The Dragon King Would Like to Battle", or more recently "You are Challenged by the Dragon King"
(The official translation keeps changing every game, haha...)
Edit: It's probably too late to say this, but the title of the premium bonus short story in volume 2 「おや？ メラクのようすが……」, translated as "Oh? Merak seems..." is also meant to be the stock "What? (Pokemon) is evolving!" phrase.