The Wolf of Ash and Fire

Horus gripped one of the warlord’s mechanised arms, one bearing the spinning brass spheres and crackling tines of its lightning weapon. The arm’s strength was prodigious, but centimetre by centimetre Horus forced it around.
Lightning blasted from the weapon, burning Horus’s hands black. Bone gleamed through the ruin of his flesh, but what was that pain when set against the loss of a father?
With one last herculean effort, Horus wrenched the arm up as a sawing blast of white-edged lightning erupted from the weapon. A searing burst of fire impacted on the Mech-Warlord’s forearm and the limb exploded from the elbow down in a welter of blackened bone and boiling blood. The beast grunted in surprise, dropping the Emperor and staring in dumb fascination at the ruin of its arm.