If you want to buy treasure cards visit Harold Argleston in Wizard City Library or Zan’ne in Krokotopia. When you buy treasure cards  go to your spell deck in the menu or press “P” on your keyboard and add the treasure cards to your spell deck.

When you are in the battle  if you don’t like your cards or you want to use a treasure card Right Click a weak card in your deck. That will delete the ones in your hand, then press the “Draw” button and click on the treasure card. You can drawn up to three Treasure Cards per round.