One of the most mysterious characters to achieve wide popularity in the Magic fandom is Terisiare's scourge Marit Lage. As the MTGSalvation wiki puts it, "Marit Lage was a powerful sorceress who existed during the Ice Age. Although she was not a planeswalker, Marit Lage was able to travel to and from planes and possessed other characteristics of planeswalkers. Little is known about her life, her fate, or what exactly she was; all that is known is that she and her followers did a lot of damage to Dominaria, and her defeat left her frozen in an icy prison beneath the sea."
Marit Lage was associated with the color relationships between blue, black, and red in Ice Age block, her two namesake cards were blue and red enchantments that hosed the other color, and of course Dark Depths produced a token that was an Avatar of her in Coldsnap. Now, getting represented (more or less) on a new card is typically the holy grail for old, obscure Magic characters, but with so much of her story untold and intriguing, a recent visitor to Mark Rosewater's Tumblr blog had to ask about her.
When the mouthful-of-a-name user bonzupippinpadaloxicopolis asked, "We will ever see Marit Lage again or learn anything more about Marit Lage?" Rosewater said:
Who hear would like to hear more from Marit Lage?
Most everyone of the 62 notes on the post were overwhelmingly positive about the notion. In the comments, krishnath noted, "Marit Lage was essentially the first time 'Cosmic Horror' made an appearance in M:TG."
My take on Tumblr: "What was Lage anyway? Warped, eldritch planeswalker who lost her spark? Eldrazi trapped on Terisiare? But yes please, more blue-red Lage stuff/evil precarious weather alteration magic."