Tu ne crois pas si bien dire. Voici un extrait d'une réponse de WotC à son sujet.

WotC :
''The Argivian scholar Arkol thought Marit Lage was a planeswalker, but he was wrong. What's known about Marit Lage is that she is a being of immense power, able to move across the planes but not by the same means planeswalkers can. She is not native to Dominaria, and could justifiably be called a demigod. She is mentioned in passing a couple of times in The Eternal Ice, a Magic novel by Jeff Grubb. It's implied that she wreaked havoc on Dominaria at some point, and it's clear that she had a human following (see the flavor text of Brine Shaman, Curse of Marit Lage, Wrath of Marit Lage, and Dehydration). One interesting footnote about Marit Lage is that the cards that bear her name penalize black's allied colors rather than its enemy colors.''