Cumulus rexes are cloudy elementals with the appearance of bearded men wearing billowing robes. Their bodies seem to be made of pure, blue solid air. In battle, they protect themselves and other monsters with Magic Barrier and can call for backup from sky fries. In Dragon Quest IX, sky fries do not appear, but they have gained the ability to call down lightning. Their description also states that they are attended to by Hell niños.
Cumulus rexes are also the target of Quest #121: A Cloudless Skye. They must be defeated by a character wielding a Miracle sword or Über miracle sword and will eventually drop a clump of cloud. The quest can be repeated as many times as possible.
The CloudKing is a two-star member of the Element family with a weight of 4. It naturally learns Infernos, Barrier and Surge. Its in-game description reads "When its cloud body is touched, it's a strange sensation."
Cumulus rex appears as a B-rank monster of the Inorganic family as part of the Terry's Wonderland 3D event. It can be synthesised at the Ancient Shrine by combining Dancing flame Might and Frostburn Might together. It eventually became recruitable during Part 4 of the main storyline from Chapter 2, Episode 2: Signs of Treasure. The cumulus rex can participate in Thunderbird's Battle Road as a party member.