Metal Skull
The Metal Skull is an EPIC pet that is available from the Titanium Egg found in the Tech World. It has a 0.03% hatch rate.
The latest Pet Simulator X value list for Metal Skull can be found below:

Regular
💎 135

Golden
💎 392

Rainbow
💎 1,100 (1.1k)

Dark Matter
💎 3,700 (3.7k)