Hero Upgrading

Keepsakes redirects here; scroll down to Evolving for those.

Upgrading
Upgrading improves a hero's HP, ATK, and DEF (thereby increasing power).
 * Heroes can only be upgraded to match your level, never higher.
 * Upgrading cost both Copper and Souls.
 * The costs increase with each level.
 * Costs are also based on the star level of the hero.

Advancing
Advancing a hero unlocks stat bonuses and upgrades to their skills. It also adds a small amount to their HP/ATK/DEF and Qualities. Advancing is not guaranteed. There is a percentage chance of success that will be shown along with the costs. If the advancement fails, the next try will be increased, usually (but not always) by half that original percentage at that level. For example, if the original chance is 12%, failure will cause the next try to be at 18%. If that fails, it will increase to 24%, and so on.
 * Only 4-star and up heroes can be Advanced.
 * 4-star heroes can be upgraded to +4, 5-star to +5, and 6-/7-star to +6.
 * Advancing costs Copper and Advanced Pills
 * The costs increase with each level.
 * Costs and success percentage rate are based on the star level of the hero.
 * Every hero has the same +1 and +2 bonuses: HP +30% and ATK +10% respectively.
 * +3 and +6 upgrades increase the effectiveness of the hero's passive ability.

Evolving
Evolving (and Demonizing) a hero increases all their stats that weren't 0 to begin with. At any level, a 7-star hero will have higher stats than their 6-star equivalent; the same is true of 6 to 5. Below is a list of the heroes that require the generic Keepsakes instead of one with their name on it. Generic Keepsakes are most often in the Jade Shop but are also granted at certain win milestones in the Devil War.
 * Only 5- and 6-star heroes can be Evolved.
 * Evolving costs 500k Copper and 30 Keepsakes.
 * The Keepsakes required for each hero are set and can be previewed by clicking the Evolution/Demonize button on their page. See below for further information on Keepsakes.
 * Evolving from 5 to 6 stars requires the hero to be level 50 and fully Advanced to +5. Evolving from 6 to 7 stars requires the hero to be level 60 and fully Advanced to +6.
 * Evolving to a 6-star unlocks the 6th advance skill, a second upgrade to the hero's passive skill.
 * Evolving to a 6-star is guaranteed; Evolving to a 7-star starts at a 20% chance.
 * Upon becoming a 7-star, men get the prefix 'Devil-' and women get the prefix 'Ghost-'.
 * Not all 7-stars are treated equally. Some receive a character redesign. These same characters also receive a boost to their main ability upon Demonizing. Another correlation: none of the heroes in the list below are a 'special' 7-star.