Card Evolution involves fusing two level 10 cards into a more powerful version of that card, with a new max level of 20.  Once you have a Universal 4 or 5 Star Card, it can also be used as material for it's respective card.  Evolved cards will often have increased Cost as well, though there are some exceptions. Only One Star through Four Star cards can be evolved normally. At times an event will be present allowing you to evolve Five Star cards. Once evolved, your card will be assigned a random D Rank skill. This skill can be changed by using Skill Shuffle.

In order to evolve cards you must ensure that both of the cards involved in the evolution have been removed from all of your decks.

Evolution Cost Chart
Number of Stars Cost to Evolve
One Star 120,000 gold
Two Star 160,000 gold
Three Star 200,000 gold
Four Star 300,000 gold
Five Star 800,000 gold