Marik Ishtar is a character that's suspected to be coming soon. There are several files found in the game showing a character selection icon, and a player profile icon. Similar to Yugi Muto, he has an alter ego called Yami Marik. His Yami version is more likely to be an unlockable character to avoid having 2 of the same character. Marik Ishtar might make an appearance through a mini event just like the Yugi Muto event.
Based on the anime, Marik Ishtar takes control of other people and use their decks to duel and does not duel himself, unless he is in his Yami Marik form. If he were to appear, he could be bringing other gravekeeper monsters like Gravekeeper's Descendant, similar to Ishizu and Odion's duel rewards.
It's likely we're getting a box with Gravekeeper stuff in it in the nearish future anyway. They need to mass-release Necrovalley regardless, and even the RL Speed Duels have a couple of Gravekeeper cards we lack. (And are getting more soon.)
SP drunkan 19days ago
Some people say he wasn't that relevant and that he barely dueled. But honestly, I don't think he is a bad character at all, they are going to make Umbra & Lumis playabale and they only dueled once. ^^ not that it matters, really. They are good characters.