EDIT: Here is more info about the unlocking process. Cyborgmatt has some info as well. It seems that you will be able to hatch a mount for your Smeevil using Critter Eggs and change the look of your Smeevil by feeding it Smeevil Treats. Possible outcomes are a crab, a mammoth and a bird. My personal guess is that you will be able to get the eggs and treats by playing the upcomming Compendium Game Mode which Cyborgmatt found in the files. Spoiler: Smeevil Mounts Aka the Tauntaun! D'awww It only wants to shake hands Source: Workshophatemachine from reddit.