Multiple skeletons can be imported into a single Spine project, so you can play the animation of the bonfire skeleton and the character skeleton to play simultaneously on the Spine editor. However, I assume what you are looking for is a feature to add other skeletons to a skeleton as instances. Currently you cannot do that on the Spine editor, but you can achieve it at runtime. For example, you can follow a skeleton of a torch which has a loop animation of fire to a skeleton of the character's hand.
For your information, we have the idea of adding such a feature to the Spine editor on our roadmap:
https://github.com/EsotericSoftware/spine-editor/issues/8
There is also an idea to improve the Preview view to allow defining an animation sequence:
https://github.com/EsotericSoftware/spine-editor/issues/371
If it is realized, it would be useful when you want to combine a loop animation with other animations. If you have anything you want to add on these issues, please feel free to add your comment on GitHub.
