The assets are made by Kay Lousberg.
Check out these cute stylized assets created by Kay Lousberg. The best part, aside from how adorable they are, is that they're absolutely free.
There are now 5 packs and an animation kit made by Kay, but the artist promised to publish a new pack in the next few months.
For now, you can get some skeletons and put them in a dungeon, Medieval or Halloween environment, or wherever your imagination takes you with Kay's assets. The files are compatible with most DCC software.