Mythic upgrade Stones are used to upgrade Mythic Gear to Mythic Tier 1 (T1), Mythic Tier 2 (T2), and Mythic Tier 3 (T3). You need T1 stones to upgrade Mythic gear to Mythic Tier 1, T2 stones to upgrade Mythic Tier 1 to Mythic Tier 2, and T3 stones to upgrade Mythic Tier 2 to Mythic Tier 3.
To upgrade your Mythic item you will need 1 Stone per one item, and the stone will be consumed in the process. To use the Stone select the item you want to upgrade and choose the Strengthen button.
How to Obtain
Mythic upgrade Tier 1 Stones will start to appear in your AFK rewards chest after beating stage 20-60, Mythic upgrade Tier 2 Stones will start to appear in your AFK rewards chest after beating stage 25-60, and Mythic upgrade Tier 3 Stones will start to appear in your AFK rewards chest after beating stage 29-60. They will also appear in the Misty Valley's treasure trove, as well as both the Store and Guild Store, available to buy for Diamonds and Guild coins, respectively. Players are limited to 2 Tier 3 Stones a month in the Guild Store.
The aforementioned stones can be obtained as quest rewards by beating certain campaign stages. You can also obtain the Tier 1 Stones from King's Tower Rewards for completing the quest to beat certain floors (100, 120, 140, 160 and 180), and as rewards in Peaks of Time or buy them in Special offers.