Traits are a set of three passive bonuses that can be unlocked to improve your Troop cards.
The majority of Traits you can earn related to improving Skills (stats): for example, gaining +1 Attack for each Blue Troop in the team or status effects (such as being immune to Burning). Each Troop has its own set of Traits.
Traits can be unlocked only with Traitstones. Each Trait takes a specific combination of Traitstones to unlock (increasing in total cost for rarer Troops), and each Troop's Traits must be unlocked in order from the Traits page in the Upgrade menu.
Unlocking a Trait on one Troop does not unlock it for others - for instance, unlocking the Sturdy Trait on Rhynax does not unlock it for the Chimera or any other Troop that can have Sturdy.
Legendary or special Traits
Legendary Traits are especially strong Traits that are each only found on one Legendary or Mythic Rarity Troop. These Traits are unique to the Troop and are quite powerful so come with a high Traitstone cost!