Q: Do pillars/pends/deck mark/"other" cards count as off-element cards for this ruleset?
A: Yes
Q: Do i need to use a mark corresponding to the element i chose?
A: No, you may use any mark you wish.
Due to verifer being judged incorrect & the simplicitly of the second question's answer, it seems the TO read "deck mark" as "mark card" in the first question. Currently the FAQ implies that if my element is darkness, setting mark to entropy will reduce my upgrades by 2. This isn't clearly stated in the first post's rules
I'm going to assume this is the case & update the verifer accordingly (not count different mark against upgrades) (& still awaiting approval, so all this rule analysis is speculation)