They appear during the Eye of the Vortex campaign when a Dark Elf faction begins a Ritual. They will spawn near a ritual site and will attempt to raze it, attacking anything else in their way. They are automatically at war with the Dark Elf faction that started the ritual.
They were also involved with the Chaos Invasion in Mortal Empires where they spawned in the sea to harass the factions in Naggaroth. But they were removed from the Chaos Invasion in December 2020.