Runes are items that a player can equip that grant bonuses to defenses, abilities, pets or other heroes. Runes have distinct rarities, but unlike other items, runes do not have a level requirement that must be met in order to equip them. Once owned, runes must be unlocked with a gold fee before they can be equipped. Once a rune of a given rarity is unlocked for a hero, any other heroes may use that rune.
Runes have an unlock cost before they can be equipped:
1/8 (Common) - 0 gold
2/8 (Uncommon) - 250 million gold
3/8 (Rare) - 750 million gold
4/8 (Epic) - 1.5 billion gold
5/8 (Legendary) - 5 billion gold
6/8 (Mythical) - 12.49 billion gold
7/8 (Transcendent) - 62.49 billion gold
8/8 (Godly) - 249.9 billion gold
Runes can be unlocked by selecting Use for a given rune, provided the player has enough gold.
Runes are equipped/un-equipped after opening your Inventory, and navigating to the Runes tab. On PC, you may double-click or press "E" to select a rune to equip or un-equip. The blue circles are for runes for abilities, the green circles are for runes for defenses.
Selecting "Equip Rune" will bring up a page where you can select any from any rune you have unlocked, as well as what equipping the rune does.
Information regarding runes was collected and compiled from these sources: