The most desirable tend to be Disney Lorcana' s Enchanted cards, which feature special foil treatments and aren't found in most packs
Using an Ability : If you have a character in play that isnt exerted, or you play an item, you can then play the ability on the card for any cost detailed on it
However, the next set for the Disney game, Ursulas Return, will feature cards that will allow players to Shift their characters without paying an ink cost
Several cards featured in Ursulas Return - including Ursula, Erics Bride and Diablo, Devoted Herald - feature the Shift keyword but allow players to avoid paying ink altogether, in exchange for players having to discard a certain type of card/s to pay to shift them in instead
The difference is that while they have an ink cost on them, there is also an extra block of text in the description area of the card which details that you can exert a character (turning them sideways and opening them to attack) of a minimum cost in order to play the song card for free