- "Imagine that. Your limbs removed, replaced with spark-whips and nests of claws. Eyes bored from your skull and stained glass in their places. Your heart and organs fixed with stimm injectors and neuropathic glands. And then, proud in your new body, what remains of your drooling waste of a mind will be turned to the good of the Imperium. With a word of my command, you'll willingly fling yourself into the jaws of hell, a berserk flesh-machine bound for a long, long death."
- —Celestian Superior Miriya of the Order of Our Martyred Lady
An Arco-Flagellant is a specialised form of Servitor, created from an Imperial citizen who has been condemned to the capital punishment of Arco-Flagellation. In battle, Arco-Flagellants are pumped full of a cocktail of narcotic stimulants that transforms them into frenzied whirlwinds of destruction utterly impervious to wounds. An Arco-Flagellant is unleashed on the enemy in a suicidal charge that causes a maximal amount of damage. They are used individually or in packs by Inquisitors of the Ordo Hereticus and the Sisters of Battle as disposable terror shock troops.
Arco-Flagellants are human beings who have been condemned by Imperial justice to death, but whose crimes are not so severe that they are behind all hope of redemption. Such criminals will be put to a merciful death after a lengthy and extremely excruciating ritual of torture intended to purify their souls, so that they may still find peace alongside the Emperor of Mankind in the afterlife. The sentence of Arco-Flagellation is only delivered to criminals on technologically advanced worlds due to the advanced resources it requires.
A penitent condemned to arco-flagellation will be handed over to the Adeptus Mechanicus, who will lobotomise him and replace both his arms with cybernetic weapons, most often a pair of heavy industrial shears or a pair of Electroflails. They will then graft a whole battery of chemical injectors directly onto his spine, and install a Pacifier Helmet which contains a crude Mind Impulse Unit, designed to control the cyborg.
As long as the Pacifier Helmet is active, the Arco-Flagellant remains dormant, with what little remains of his mind filled with the hymns and holy iconography of the Ecclesiarchy. He will only be able to shuffle around if ordered to, but will otherwhise remain immobile in a deadened bliss. Once dragged into battle, the Pacifier Helmet will be deactivated, and the injectors in the Arco-Flagellant's spine will start unleashing their cocktail of drugs (often a volatile mix of Barrage, Frenzon, Slaught and Spur) into his body. This cocktail will grant the flagellant enormous strength, speed and stamina, and will plunge him into an uncontrollable killing frenzy fuelled by the drugs and the terrible pain of his crude bionic grafts. The helmet will then only allow him to see any being who has not been tagged by his controller as friendly. The Arco-flagellant will rush toward the nearest living creature it can see and rend it to pieces, utterly uncaring of his own wounds or survival. He will continue to attack in this berserk manner until he has been mortally wounded, or his metabolism finally collapses under the assault of the deadly mix of chemicals constantly injected into it to maintain his frenzy.
Arco-Flagellants are either detached individually to the service of those Inquisitors who need an unsubtle tool for a vital task like the eradication of a nest of Heretics, or gathered in groups and unleashed upon the enemies of the Emperor in an orgy of slaughter that would put a Khornate Berserker to shame. Although the Sisters of Battle readily use Arco-Flagellants, and rejoice in seeing criminals finding their redemption in death, they keep a wary distance from the creatures, and only use them when they are past considerations of collateral damage. To the Arco-Flagellants, any living being who has not been specifically tagged by their controller as friendly is an enemy, and they will kill it accordingly, be it a true opponent or simply an innocent bystander.
- Simeon 38X - Simeon 38X is an Arco-Flagellant. Before his arco-flagellation he was a human male named Erin Octavus, a Grox farmer native to the Agri-world of Standalone. A sufferer of Gathalamor Syndrome, a condition in which subjects become determined to sacrifice themselves in the name of the Emperor, Octavus believed he was tainted by evil. After several attempts to placate and purge the farmer failed, Octavus, spurred on by his hallucinations, attacked Cardinal Simeon, for which he was tried and sentenced to Arco-flagellation. Octavus was renamed Simeon 38X after the Cardinal who had condemned him, yet he still suffered from Gathalamor Syndrome (it was speculated that his Pacifier Helm actually worsened his condition), which resulted in him not always responding to his trigger word, "Exculpate". This resulted in bloody consequences several times, but most notably during his service to Inquisitor Steinbeck. Following the grisly death of several members of the Ecclesiarchy as a result of this quirk, Simeon was almost terminated as too dangerous to be controlled. The Witch Hunter Tyrus intervened, granting him a stay of execution. Simeon was given a re-trial and sentenced to deathmasking. After this, he was held in stasis aboard Tyrus's own vessel, a ready instrument to be unleashed upon the Inquisitor's most hated foes.
- Damien 1427 - Damien 1427 is a human male and an Arco-Flagellant. His trigger word is "Purgatus" and his true name has been expunged from Imperial records. He was once a citizen of the world of Siluria IV. Later, he became an iconoclast and gathered a heretical mob in the wilderness areas of that planet. After defying the Cardinal of Siluria IV and speaking out against the Planetary Governor, Tyron Rex, he was arrested and sentenced to Arco-Flagellation. His current status is unknown.
- Codex: Witch Hunters (4th Edition), pg. 28
- Dark Heresy: Blood of Martyrs (RPG), pg. 122
- Inquisitor (RPG) pp. 138-139
- The Inquisition: An Illustrated Guid by Nick Kyme, Lindsey Priestley, George Stirling, pp. 8-9
- The Inquisitor Sketchbook by John Blanche, pp. 42-43
- White Dwarf 260 (US), "Inquisitor: Simeon 38X", pp. 17-18