Third War for Armageddon
Skarfang took part in the Third War for Armageddon with his Gargant Big Mob. Skarfang had three warbands under his command, as well as 6 Gargants. The only engagement we know of is between Skarfang's Gargants and the Legio Crucius, with Warlord Burzuruk supporting the Orks. The result of the battle 8 Gargants and 6 Titans destroyed.
Skarfang's base, the planet Ghorala, found itself in the path of Hive Fleet Leviathan in the Octarius War. When the Tyranids arrived, their bio-ships stumbled into the extensive Ork mine fields disguised amongst Ghorala's asteroid belt, and many were torn apart. Ork Gunships then engaged the surviving Tyranid bio-ships, and destroyed them all, despite being badly mauled themselves. However, amidst the chaos, a single bio-ship slipped past the Ork blockade and hurled itself toward Ghorala. It managed to rain thousands of Mycetic Spores onto the planet's equatorial planes below before it was torn apart.
The Tyranid swarm on Ghorala found itself vastly outnumbered by the Orks, and adapted in order to survive. At first, they preyed upon isolated Ork patrols, but the Orks soon took to scouring the landscape in massive mobs. The Tyranids then changed tactics and engaged the Orks in the open to maximize the carnage. But the Orks' number quickly gave them the advantage in these skirmishes, so the Tyranids would retreat whenever they were about to be overrun, and hide in nearby caverns or burrow underground to avoid detection. At night, the swarm would re-emerge into the corpse-choked battlefield to feast upon corpses from both sides before returning to the digestion pools secreted in the planet's rocky mesas. Slowly but surely, the Tyranids' number began to grow.
With its number increased, the Ghorala swarm became aggressive again. But the increased violence soon attracted Skarfang himself to the battlefield. Whenever his guttural warcries were heard, the Orks would attack would renewed vigour; and whenever the Tyranids looked to be on the cusp of victory, he would be able to turn the tide. In response, the Tyranids created Lictors with the express purpose of eliminating Skarfang. Within days, the Lictors tracked their quarry, but packs of Squig-hounds foiled all attempts to get close enough to assassinate Skarfang. The Tyranids then attempted to goad Skarfang out into the open. They executed a number of feinted attacks on the Orks, approaching from different directions to within arm's length, and each time withdrawing before the Orks could retaliate. On the tenth such retreat, Skarfang's temper could take it no more, and the Warboss ordered his mobs to pursue the fleeing swarm.
As the Orks pursued their quarry, they rode headlong into a sudden, blinding mist, which turned out to be toxic fog generated by Tyranid Venomthropes. The Ork convoy ground to a halt as vehicles either lost control and ploughed into each other or skidded into rocky outcrops. Choking and coughing, the Orks climbed out of the wreckage. Skarfang himself stumbled across the Venomthropes and killed them, causing the fog to recede. The Warboss found himself surrounded by the corpses of eviscerated Orks, and the Lictors that had stalked and dispatched them through the mist. As the Lictors closed in on their true quarry, Skarfang revved his chainblade into life and charged, roaring his defiance. He managed two steps before a dozen mantis-like claws pierced his form and tore him asunder.
With Skarfang dead, vying bosses soon fought amongst themselves to determine who would fill the power vacuum. The now disparage forces of Orks were isolated and destroyed in quick succession by the Tyranids in a matter of weeks. From the biomass gained on Ghorala, the Tyranids infestation quickly began to spread once more. The Ork worlds of Derragon and Keltor fell shortly after, and even Octarius found itself embroiled in war.