Koala
The Koala is an EXCLUSIVE pet that is available from the Exclusive Pets Egg, with a 50% chance of hatching. It was made available in the Pixel World Update.
The latest Pet Simulator X value list for Koala can be found below:

Regular
💎 1,900,000,000 (1.9b)

Golden
💎 Not Available

Rainbow
💎 Not Available

Dark Matter
💎 Not Available