The god of Murder and Death. Very little is known about him.
We have not seen an incarnation of this god yet.
The only known worshippers we've encountered are the gnolls in the wilderness near Veretas. One of the gnolls appeared to be a cleric that used its holy symbol to pray to Usallo and offer itself to become a withering gnoll.
In a later gnoll attack, all of the gnolls seemed to be empowered by Usallo to be able to break the impenetrable Tiny Hut created by Sindri.
A pack of gnolls attacked some bandits and we rescued them. One of the gnolls was a cleric that ended up using its holy symbol to pray to Usallo, offering itself up to become a withering gnoll, though we defeated that, too. Later, more gnolls prayed for power to get revenge on us. Usallo empowered them enough to destroy something invulnerable; the tiny hut that protected us.