Masvirik consumes the light, embodying our fears of all that slithers through the dark and cold. On the one hand, he embodies the warm-blooded fears of reptiles and venomous vermin. On the other, he embodies the reptilian fears of cold and death. His minions include corrupted lizardfolk, dragonborn, and kobolds, along with undead reptilian creatures and fiends who thrive on cold instead of heat
Masvirik is imprisoned beneath Haka'torvhak, and
his influence is felt across Q’barra. His speaker, the
dragon Rhashaak, is bound in Haka’torvhak; the reptilian rakshasa Asshalara represents Rhashaak on the
Bleak Council of Ashtakala.
Source: Chronicles of Eberron
In the Age of Demons, the region now known as Q’barra was the domain of a fiendish overlord of terrifying power. He drew the light from the sky, and so his slaves called him Masvirik, “the Cold Sun,” cousin to Tiamat. Masvirik has power over creatures of scale and fang and venomous things that slither through shadows. The dreaming priests of the Masvirik’Uala say that the Cold Sun formed kobolds and troglodytes from lizardfolk stock, creating beasts that were more vulnerable to his power. The existence of these creatures in distant lands calls this into question, but kobolds and troglodytes make up a larger percentage of the Poison Dusk than any other race.
Like many of the overlords, Masvirik’s arrogance was his undoing. The dragons and couatl freed the lizardfolk from his influence, and they rose up against him. In time the Cold Sun was cast down, bound beneath his obsidian citadel, and trapped by the Silver Flame. The couatl sacrificed their lives to kindle that flame, but the dragons remained.
In time they dispatched the black dragon Rhashaak to watch over Q’barra. He was accompanied by a host of dragonborn soldiers, hand-picked from the legions of the Light of Siberys. These sentinels established garrisons at various demonic sites across the region. The worst of these was the resting place of Masvirik, which they renamed Haka’torvhak. Rhashaak made his home there, with the best of his soldiers, and there they waited.
Masvirik has followers among the Lords of Dust, but he doesn’t have a prakhutu on the Council of Ashtakala; Rhashaak is his voice, and the dragon is bound in Haka’torvhak. The Poison Dusk are his minions, and at the moment he has little influence beyond Q’barra.
Masvirik has some overlap with Zehir, and a Dungeon Master who wishes to place Zehir in Eberron could use the Cold Sun for this purpose. Masvirik could easily share Zehir’s rivalry with his fellow overlord Tiamat.
Information about Masvirik is extraordinarily scarce. Even the dragonborn of Ka’rhashan remember little about this ancient fiend, having focused their attention on their battles against the Poison Dusk. The lizardfolk are among the only people who know anything about the overlord, and so far they haven’t shared this lore with outsiders.
Source: Dragon 185