I created a summon Field Guard treasure card to use in ranked pvp. It was the only treasure card i put in my deck. But even when i had discarded all of my spell cards, it still wouldn't let me draw anything. Is it because summon minions aren't allowed in ranked pvp, or because they can only be used as your first move or something? Because when I tried it in practice pvp it worked out fine.
It worked in practice pvp because there is no loss or gain from it, in ranked it is the opposite. Practice pvp is probably the only other time you are allowed to use a summon tc minion besides pve, since there is no harm in doing it. In ranked, you are not allowed to use them at all, as shown by the symbol on the card.