Gáe Bulg

Beware The Red Spear

Yamaoka Naoko was a master of The Scarlet Arts. She was accomplished in The Strain of Profanity. During her time as the Matron of The Children of The Fiery Lock, a time referred to as The Red Years, she developed a spell that not only demonstrated her brutal methods, but remains the object of fear for many who face masters of The Scarlet Arts.
While Naoko considered the spell to be part of The Strain Of Passion, by definition it is profane. She developed the spell to inflict pain. It wasn't merely to kill, it was torture. To this day, the spell is only used as a last resort, and can have a profound effect on the one who casts it.
During this time, Naoko and her cult resided in Ireland. She grew close to the culture, even having a brief marriage with an Irishman. Through his stories, she fell in love with the story of Cu Chulain, and a peculiar weapon that left its victim in ruins.

Casting the spell

Pronounced (guy bull-guh), the spell is named after the spear of Cú Chulainn, and its effect is inspired by a special technique the warrior was taught. It begins with The Static, linking veins with an enemy as many offensive spells in The Scarlet Arts do. The next step is using a combination of techniques called Coagulate and Crimson Javalon.
By thickening the blood, one can solidify it into dark red crystalline structures. Using the static, they can shake it into a spike (Javalon) and hurl it at their opponent. It's the final trick of the spell that made Gáe Bulg unique. Another spell is blended into the mix: Blood Pathogen.
The blood pathogen spreads a given state through any source of blood touched, here by the javelin. Should you be skewered by the spear, the same crystalline barbs will spread, "coursing through the highways and byways of [your] body so that every single joint fills with barbs."

What Does It Do?

The spell causes blood in the bloodstream to crystallize, forming tiny barbs that pierce the vessels. These barbs skewer muscles, nerves, and build up throughout the body in an extended process of agony. The victim is unable to stop it as the spear needs to be cut out of the body to be removed.
Blood takes 45s on average to cycle through the body, though this will be shorter due to the higher heart rate the stress causes. That's how long it takes at maximum before you start feeling the barbs in your heart. You'll feel it in your brain and your body will not function and obey.
It will leave you mangled and broken; a bloody mess. It is a death that one gives to those they wish to bleed slow, so they can think about their death, if the pain even allows coherent thought. This spell is taught to all Ladies-In-Waiting in the cult and it fundamentally changes those who use it.

Psychological Consequences

Even the most steadfast practitioners find it hard to even use the spell. Those who do regret it immediately. By linking veins, you feel their pain, but not as your victims do. The passion blends pain and pleasure. You relish the sensation as they convulse, blood spilling from their bodies.

This changes how one views death, and morally compromises a person. It's easier to kill, and justify it as a better alternative. It's easier to inflict pain, cause it's not the worst you could inflict. When the spell is done, you're left with the memory, and it never sits well.

Fun fact: On The Nature Of Spells

New spells in The Prestige are rarely new, but are merely rediscovered or reimagined spells lost to time. These spells were lost and eventually resurfaced due to experimentation and resurfacing texts.
This spell is important because it is actually a completely new spell. It was created by combining several other spells and techniques to achieve an entirely unique result. The combination of coagulate, crimson javelin, linked veins, and blood pathogen makes Gáe Bulg one of the most brutal and painful spells in The Prestige, and nothing has ever been seen like it before or since.
New spells appearing cause a massive upsurge in using the spell. With Gáe Bulg being a spell in the strain of profanity, its usage is often deemed as a last resort. Even then, there is a common guilt felt on casting it due to the amount of pain and brutality inflicted on the victim.