I know no one asked, but I feel like I need to do this regardless since there is a gap in the rules:
Clarification: "Other" cards like Quantum Pillar count as a separate element.
ALL cards count as cards used towards their element, including Pillars, Pendulums and Mark cards. Mark cards count towards cards of their respective element, not "Other".
I realize it's a bit late, but I wanted this cleared up before the start of the tournament. Adding to the OP now, too.