Mara could easily be placed in an "antagonists" section but considering she isn't a very effective villainess and was a good friend of Urd's, her "profile", so to say, is in the friends section.
Mara, or, as it is written in certain versions, Marller, or Marla, is one of the main antagonists in the series that continually shows up. She's full-blooded demon with a seemingly nasty attitude. Her transport of choice are CD's and it just so happens that one of her main weaknesses is music. Whenever Mara hears rock (in the Japanese version) or disco (in the English version) she dances, whether she wants to or not. Another weakness that Keiichi and co. often use to their advantage is Mara's unfavorable reaction to good luck charms. These two things put together don't seem to leave much room for a demon victory.

Mara, however, is desperate for a promotion and at one point becomes somewhat of a lackey for Hild. She also is a complimentary servant for the Lord of Terror. In both cases, she ends up suffering the usual lackey abuses and does very little to hinder the goddesses.