Thread:Emmic/@comment-12281387-20140118193024/@comment-4292163-20140118194659

The only limitations on deckbuilding are that the deck be 52 or more cards, including at exactly 1 Flag and at least 1 Monster (to be used as a Buddy). As with Vanguard you're only allowed to run 4 of each card, though your Buddy doesn't count towards this so you can (and probably should) run 5 copies of your buddy.

If you're wondering how many of each type of card to use, that's hard to say since the game isn't out yet. For now I'd recommend looking at what the Trial Decks are doing - 28 Monsters (including Buddy), 14 Spells, 6 Items, 3 Impacts and a Flag.