i think that as you level up maybe every certain number of levels you get a treasure card equip slot for your decks maybe it goes by the level of the deck
the spots let you equip a treasure card that will come up as normal cards but is not used up when you use it
lv 20 1 slot lv 40 2 slots lv 60 3 slots lv 80 4 slots lv 100 5 slots lv 110 6 slots becomes lv 120 when the cap is raised
