The Servants are the Seven Chaos, Chaos is Power, Enriched by My Will...
— Dr. Finitevus' accessing the Master Emerald's power with his hex.
Dr. Finitevus' hex is a move that appears in the Sonic the Hedgehog comic series published by Archie Comics. It is a powerful spell created by Dr. Finitevus that was used in his grand scene to destroy Mobius. Once someone (or a power source), is infected with the spell, they are subject to Finitevus' will. Dr. Finitevus placed the spell on the Master Emerald to block any Guardian's link to, and abilities to harness, the Emerald. Finitevus was the only person who could access its power, and did so using a slightly modified version of Tikal's Prayer. Dr. Finitevus tricked Knuckles into tapping into the Hex via the Master Emerald, putting him under the doctor's will and convincing him to turn into Enerjak.
Finitevus went through a along development process to complete his spell. It's main pourpose was to turn a host into Enerjak. He setled on Knuckles and tricked him into tapping into Master Emerald with the Hex in it. The moment he touched the Emerald, Knuckle's intentions bent to Finitevus' ideals. The hex scrambled Knuckles' mind, leading him to become a willing participant in Finitevus' plan and allowed himself to become Enerjak. Thanks to the hex, Knuckles could turn into Enerjak rapidly unlike the Enerjak's before him.
Sonic the Hedgehog, planning to save Knuckles, attempted to neutralize him the same way as Perfect Chaos; by canceling the negative Chaos powers of Enerjak with the positive aura of Super Sonic. Dr. Finitevus was surprised Super Sonic could use the Master Emerald's power without the hex having any effect on him, as he should not have been able to draw power from the gem. It remains a mystery how he was able to turn into Super Sonic; Finitevus mentioned a dissection of Sonic could find an answer. While Super Sonic's aura did have an effect on Knuckles, it could not break the Hex's control.
When Julie-Su demanded Dr. Finitevus to break the Hex, he explained he couldn't. Expecting a plucky resistance to "save" their beloved Knuckles, Finitevus locked hex, leaving him unable to stop the fight between Super Sonic and Enerjak even if he wanted to. The only way to break the Hex and his control was for someone to sacrifice their own life. Finitevus believed no one would be foolish enough to sacrifice their own life to break it. He was proven wrong, as Julie-Su, Archimedes and Locke all volunteered to do so. He attempted to stop them, but Archimedes teleported Finitevus away. Locke elected to perform the ceremony, wanting to make amends for all he had put his son through. Locke's sacrifice of his life-force broke the hex and caused him to be consumed in energy from the Emerald, leaving nothing behind. Knuckles finally succumbed to Super Sonic's aura and returned to normal.
To be sure there would no ill effects on them because of the hex, Sonic and Knuckles were included in a ceremony by Merlin to remove the curses placed upon them, along with Tails, Mina Mongoose and Mighty. Merlin told them the hex was very powerful and should have stopped Sonic from transforming into Super Sonic. When Sonic asked why the hex had no effect on him, Merlin told him that was his next order of business.