There are quite a few unknown planar entities that have some relation to Norrathians in one way or another. These lesser planar entities made themselves known to a small select few. This interaction occurred throughout time, but may have only recently been uncovered. Look around Norrath in the Age of Destiny, you may find hints of these agents of greater entities. I know there are at least a few others you have yet to mention. We may never see them, but their tales may give you more planar lore.
In the case of Byzola and Dymetreax (a.k.a. Dymetreas), these entities have been recorded as far back as the Age of Turmoil and had dealings with Norrathians even further back.
Byzola is the conjoined twin of her brother, Dymetreax. Together they are known as the Twins of Torment. They exist upon the Plane of Fear and work as agents to the ruler of that plane- Cazic-Thule. They have ventured far and wide in the name of fear. They bring about pain, both physical and mental, to any creature they see fit.
In a time long past, they encountered a champion of mortal worlds who ventured to the Plane of Fear to do battle with the Twins of Torment. During that battle, Byzola was slain by the magical brass weapon being wielded by the mortal. Byzola now lies as a fetid corpse still attached to her still living conjoined brother. They were being bred by the Faceless to seize control of a quasi plane from an agent of the Plane of Hate. It has not been validated, but some accounts hint that Byzola is now an undead entity.
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I was made aware of this by the lore lovers over at Oscuris! Check them out! https://discord.com/channels/228604818057330688/641332324956373012/862412110595620915
Original reference:
https://forums.daybreakgames.com/eq2/index.php?threads/gods-of-everquest.197162/page-2#post-2166215
EverQuest - Lore of Norrath 