Class Cards can be Enhanced using spare Class Cards won from playing Wave Mode. This increases the stats unique to the abilities of that Class when playing Wave Mode. The exact increase to ability stats is shown by hovering the mouse over your Class Card.
To Enhance a Class Card, you must be in your Class Card inventory. From there, drag the card you wish to Enhance to the first Card Slot on the right.
Then, choose the card you will use to Enhance the first card, and drag that to the second Card Slot on the right. Once both Class cards are in place, click the “Reinforce” button. You will then have a stronger Class Card!
Enhancing a Class Card requires you to sacrifice a second, extra card. For best results, you should use a card of the same Class as the card you want to Enhance (like in the screenshot above). Once a card is used to Enhance another card, it is destroyed and will be removed from your Class Card inventory—so think carefully before choosing which card to use as Enhancement Material!