Merlumina was a member of the Tribe of Ancients. 1,500 years before the setting of Super Paper Mario (the only game she appeared in), she was told to protect the Pure Heart in Yold Ruins and await the hero of legend. 1,500 years later, her ghost still waited (albeit slightly impatiently) for the hero to arrive so she could give the hero the Pure Heart.
In addition to protecting the Pure Heart of Yold Ruins, it is possible that Merlumina had other distinctive authorities among the Ancients. Tippi reveals in her information for Merlumina's stained glass window in Mirror Hall that Merlumina acted as a leader among her people, and it is stated in her Catch Card that she "made a Pure Heart," possibly insinuating that she is the creator of the Purity Heart. (However, such a title is additionally stated to possibly belong to Merlimbis.) According to her ancestor Merlon, Merlumina is also the authoress of the Light Prognosticus, though players could later have Tippi mention Merloo being believed to be its writer.