A Blood Curse, also known as the Blood Pact, is when an orc or group of orcs consume the demonic blood of a powerful pit lord to gain supernatural strength, speed, resilience and stamina. The effects as well as side effects are immediate, and the symptoms that manifest from blood consumption are green skin, glowing red eyes and a considerable increase in size. Further exposure and physical change cause the skin to turn red, a greater increase in body mass, green/purple eyes, extra tusks and bone growth that breaks the skin.
Orcs under the Blood Curse are in a constant state of aggression and violence, and maintaining normal composure requires considerable self-control.
A Blood Curse is contagious; even though only twelve clan chieftains personally drank Mannoroth's blood, nearly every orc in the Horde was soon under its influence.
The effects of the curse are not limitless in duration, however. Eventually, if not given continuous reinforcement, it fades and leaves the user in a state of withdrawal.
Killing Mannoroth dispelled his Blood Curse throughout the Horde. However, their skin remains green, and they can intermittently choose to revert to their previous state of rage to increase their strength (the ability).