Gray Demons

The Gray Demon is part of the Demon Clan and is a higher being than the Red Demon. It's being used as one of Hendriksen's experiments.

Appearance
The Gray Demon is a tall being compared to a Giant's size, has long scaly arms, sharp claws and feet, and small wings. It wears a lower bottom armor and a sun-shaped helmet with a terrifying face.

History
At some point of time, the Gray Demon was killed by an unknown individual of great power as it shown to have died from a large slash wound in the chest. It is shown to have participated in a war between its Clan and the Four Races.

Few years later, its corpse was found by Great Holy Knight Hendriksen who studies Demon genealogy and biology and conducts countless experiments.

Kingdom Infiltration arc
After Ban sent Hendriksen pummeling down deeper underground beneath Merlin's ruined castle, the Great Holy Knight went to the Gray Demon's corpse and explained the four Sins Meliodas, Ban, King and Gowther about the demon which is much higher than the Red Demon, how he found it and experimented on it. Hendriksen took a blood sample from the Gray Demon's corpse and injected on himself, resulting to gain tremendous power-boost from the demon and began his counterattack by taking out the Fox's Sin of Greed.

Abilities/Equipment
According to Hendriksen, the Gray Demon is a being higher than the Red Demon itself and its blood can provide the individual access to its powers of light and a resilient body to become a stable vessel of Demon power.