Who or what is Mystara?
Solution 1:
"Mystara" is an in-joke and refers to the D&D setting of the same name. It comes to Oblivion via its lead game designer Ken Rolston who was involved in the creation of the Mystara D&D setting and authored two of the background books for it:
- The Emirates of Ylaruam
- The Northern Reaches (with Elizabeth Danforth)