Costumes are similar to a template for an alternative skin of a Hero. The respective Hero can wear the costume to change stats, skill set, class, and appearance. Costumes also permanently increase the stats of the Hero, even if the Hero doesn't change the apperance. Costumes were intended to make S1 Heroes more competitive. If you have more than one respective Hero, all profit from the stat bonus and can wear the Costume (or not). While a Hero is active in a war or raid tournament defence he is bound to that appearance; a second Hero you own could of course take a different appearance. The costume is un/equipped in the Hero Roster. The Hero Card always shows the bonus granted by the costume.
To apply any bonus the costume has to be leveled itsself and independently of the original Hero. Leveling a costume works similar to leveling a hero but is much cheaper. A costume cannot be ascended past the ascension level of any respective Hero you own. The maximum stat bonus of +5% Attack, +5% Defence, +10% Health, +5% Mana Generation is applied when the Costume is fully ascended and leveled and the special skill is at 8/8. Until then every ascension level grants smaller bonuses:
|Ascension 1||Ascension 2||Ascension 3||Ascension 4||Fully Maxed|
Heroes wearing a costume have their skill set and class changed. That is mainly to enable them to be used more flexibly and frequently. E.g. Sonya changes her class from Paladin to Druid and therefore can be used in the Trial of Nature Class Quest. The costumed Hero inherits the emblem path from the original Hero. Also only the original Hero can be emblemed with the original class emblems (therefore Sonya can only be emblemed with Paladin emblems). Emblem effects are furthermore only applied once the costume is fully maxed (levels and skills).
As of January 2020 costumes are available for the following Heroes:
|3* Costumes||4* Costumes||5* Costumes|
You can find a comprehensive overview on the stats of the original and costumed heroes here.