@duke
Yes, its only for discards from R12, which will be the discards you put in this round. Also, yes, it has to be from your team's vault, not from another team's vault.
@zawa
EC apply to all decks. You can use 6 discarded cards in total. So, in your given example, you may only use 6 mindgates in one deck, or 3 in two decks..
No, real cards take priority. So, if you do have 3 mindgates already, they will be used first, then the virtual ones.
Air is facing darkness 3 times as gravity and aether must face 3 and 2 different opponents respectively.