The Ironstrider is one of the oldest and most trusted patterns in the Mechanicus arsenal, a bipedal walker whose long, articulated legs carry it swiftly across terrain that would mire a tracked vehicle. In its Ballistarii configuration it is given over wholly to ranged destruction, its rider a single Skitarius fused to the machine by cortical dendrites so that walker and warrior move as one hunting organism.
The Ballistarii exists to kill the things other weapons cannot. Its primary armament is a pair of powerful cognis weapons, most often twinned autocannons whose disciplined bursts stitch through light armour, or paired lascannons whose searing beams punch clean through battle tanks and the hides of towering monsters. Guided by the machine's cognis targeting spirits, which calculate range and lead with inhuman speed, the rider looses death with an accuracy no mortal gunner could hope to match.
What makes the Ballistarii so prized is the union of that firepower with genuine mobility. It lopes to a commanding vantage, unleashes its guns, and strides clear before the enemy can bring return fire to bear, forever repositioning to keep the foe's heaviest engines in its sights. Deployed in squadrons, these striding hunters form a roving gun-line that can dictate the shape of a battle, denying whole swathes of the field to enemy armour and reducing prized war-machines to burning wreckage from afar.