Skins increase hero stats and change their appearance. Each hero has a Default skin that boosts their main characteristic: strength, agility, or intelligence. Additional skins upgrade secondary stats. To level up a skin, you need to use Skin Stones.
All skin bonuses stack no matter what skin is active at the moment. Equipping a skin only changes the appearance of a hero.
You can purchase skins with Skin Stones, buy them in the Skin Sale tab, or get them during special events.