Basic attributes of cards will be improved only when the card levels up. And the only way to upgrade a card is to strengthen it and gain Exp.
For cards that you'd like to evolve, keep strengthening them until they reach level 20. Because only cards at Lv 20 and above can be evolved.
- 1 target card
- at least 1 material card
Material cards will be fused into the target card and disappear after the strengthening. Note: You can use any card as a material card, but the target card will gain 15% more Exp if the material card belongs to the same element.
If material card have some levels, it will give more exp to target.
Cost for strengthen depends only on level of card and number of cards used in process:
80*card level +100*number of cards used in strengthen. So if you strengthen card level 23 with 6 cards, cost will be 23*80+100*6=2440
Cards—→Strengthen—→Tap Add or the central empty slot & select a target card—→tap Add or any surrounding slot to add 1 to 6 material cards—→Tap Strengthen
If your card will level up after this strengthening, the to-be-added attributes stats (those green numbers) will be flashing near your current attribute stats.