Mortuus
The Mortuus is a LEGENDARY pet that is available from the Geode Egg found in the Spawn World. This is the rarest pet from the Spawn World.
The latest Pet Simulator X value list for Mortuus can be found below:

Regular
💎 15,000 (15k)

Golden
💎 50,000 (50k)

Rainbow
💎 120,000 (120k)

Dark Matter
💎 400,000 (400k)