Greetings, all!
The release of the Ruinous Caverns introduced Pets and Spirits, somethign that's been on my to-do list since the beginning of ED's development.
Spirits can be "caught" automatically in the caves if you have the appropriate taming item in your inventory. These taming items can be crafted by Necromancers who have learned the recipe. There are currently only two types of Spirits and taming item available until we're sure that nothing major is going to break, then more will gradually be introduced over time as new locations are added. Hint: Railway.
As always if you've found a bug, please submit it via the Service Desk to earn yourself a Gemstone!
Akky~