In TES IV: Oblivion, beggars will occasionally say "Blessings of [one of the Nine Divines] upon ye" after you have conversed with them. They will also occasionally say "Blessings of Mystara upon ye". Mystara, however, is not one of the Nine Divines.
I've searched the UESP wiki and found nothing related to Mystara as mentioned in Oblivion.
Who or what is Mystara?
I came upon this UESP forums thread where users mentioned that it could be an easter egg, and/or a reference to "a campaign setting for the Dungeons & Dragons role playing game". Can anyone confirm/deny, or expound on how these relate to how Mystara is mentioned in this context?