Considering that in past events lvl 50 LDs popped up randomly, they might no be necessary but if lvl 50 Marik is available at the gate they might not be needed. But since the event is divided in phases I bet you will face him there (gate)
I am available at Level 50 starting from December 15th. Why are you so eager to duel me? Do you think you can endure the wrath of my Egyptian God Card THE WINGED DRAGON OF RA?
I am ready and willing to fight your Egyptian God again, Yami Marik! Bring it on, gorgeous! Oh, and thanks for always coming to Duel Links during the times when all of my homework is finished.
I am guessing you are new to the game. Knowing from my experience playing the previous events (such as toon world, Destiny board, and guardians of the gate), there were nothing to spend to play at lvl 50. So to answer your question, you will not be spending any map fragments for lvl 50 Marik.