Are these sentences worded in the best way?

FYI- Ysval is the nighthaunt. The next day, Nymia and Milsantos’s army assembled outside the Keep of Thazar and prepared to attack the undead horde in the fortress, which was shrouded in a magical gloom created by Ysval. The Firelord’s priests summoned a colossal lava elemental that demolished the Keep of Thazar’s fortifications while Aoth and the other griffon riders fought the undead and their necromancer allies. Although the nighthaunt soon destroyed the gigantic elemental, it managed to create a large breach in one of the stronghold’s walls. The Thayan forces quickly advanced through the opening and engaged the undead host, but when Chathi and the other clerics of Kossuth tried to use the torch weapons supplied by Szass Tam, the implements exploded and killed their wielders as well as everyone near them.