You can advance SR and SSR heroes in the Temple of Destiny, at the cost of the required materials. Hero advancement enhances hero quality, level cap, and basic attributes.
For those heroes not from the Temple / Abyss, check their advanced requirements in the Advancement Formula at the Temple of Destiny.
The base quality of Temple / Abyss Heroes is [Elite]. [Elite] themselves*2 = [Elite+]; [Elite+] + [Elite+] = [Epic]; [Epic] + [Elite+] = [Epic+]; [Epic+] + [Elite+] = [Legendary]; [Legendary] + [Elite+] = [Legendary+]; [Legendary+] + [Elite+]*2 = [Mythic]. After the Hero reaches [Mythic], you can continue to use [Elite+] to increase the heroes' star level. The upper limit is 5 stars.
For those heroes not from the Temple / Abyss, check their advanced requirements in the Advancement Formula at the Temple of Destiny.
The base quality of Temple / Abyss Heroes is [Elite]. [Elite] themselves*2 = [Elite+]; [Elite+] + [Elite+] = [Epic]; [Epic] + [Elite+] = [Epic+]; [Epic+] + [Elite+] = [Legendary]; [Legendary] + [Elite+] = [Legendary+]; [Legendary+] + [Elite+]*2 = [Mythic]. After the Hero reaches [Mythic], you can continue to use [Elite+] to increase the heroes' star level. The upper limit is 5 stars.