I'm not ready to play this as the DM yet, but I'd like some advice for when I am ready.
The main BBEG is Zor'Tag, a Black Greatwyrm that's a high level wizard, that's because a unique undead, & is the leader of a cult.
Zor'Tag had turned himself into a mix between a Progenitor Vampire, a Pseudo Archlich, & a Dracolich, using a special ritual that he created by combining/modifying existing rituals.
He looks like a Vampiric Black Dragon Greatwyrm, but he functions as more.
The cult he leads doesn't worship him, but instead the Primordial of Predation Doomra.
The cults name is of course the Knights of Doomra. The cults main goal is to free Doomra from his prison in the outer plains.
Doomra was originally the biological son of a moon elf & a gold dragon, but he rebelled hard thanks to never really knowing his father, but then he met Zor'Tag who was still just an ancient dragon at the time, & become his apprentice/minion, but eventually Zor'Tag & Doomra became like father & son, & so with Zor'Tag's help Doomra became a a true dragon, though with traits of both gold & black.
Long after becoming a true dragon known as the Golden Terror, Doomra when he was a Greatwyrm, gathered followers including mostly other dragons & he after much trial & error found a way to achieve something similar to apotheosis, but instead of becoming a god, he would become a primordial.
After achieving his goal to become the first mortal to ascend to primordial hood, he began doing what any good predator should & started hunting his prey, which just so happened to be gods, & other primordials.
To stop him the remaining gods of all alignments, & the majority of the remaining primordials joined forces, & gave their aid to a party of epic level adventures to build a special arrow that could only be used once, but tragically it only weakened him, rather than killed him like they hoped, so to keep him from retaining his power Doomra was taken to the outer plains where he is locked away & his cell is watched by an outer planer entity of each outer plane, for it's one of the few things that'll get an angel, devil, & demon working together.
After Doomra was imprisoned Zor'Tag gathered the remaining followers of Doomra, along with others that might be inclined to follow the newly made cults beliefs, Eat or be Eaten, the cult has different subfactions in it that take to different approaches, such as hunting prey solo, hunting prey in packs, sport hunting, & farming "cattle", but no matter if they hunt alone, hunt in packs, hunt for fun, or farm others, they are unified by these rules, no eating your fellow cultist, unless they have they have stopped being of use for the cult, or they have betrayed the cult, or they are already dead by the hands of an outsider to the cult.
Doomra despite being weakened/imprisoned, can still give his blessings/boons to his followers, but at the moment only 3 can hear him directly, & that's Zor'Tag the cult leader, along with the 2nd, & 3rd in command of the cult.
The highest ranke in the cult are the Heralds of Doomra, with it's members known as the Fangs of Doomra, or Fangs for short. There's 14 fangs, one for each class(including psion, & artificer), with the clinic as 2nd in command, & the warlock as 3rd in command.
Zor'Tag mad 13 pseudo phylacteries, in the form of powerful magic items, that are the signature weapons/relics of the other Fangs, examples such as the cleric's holy symbol, the warlock's pact weapon, the paladin's ax, & so on.
The Heralds of Doomra are all dragons, though some of them are altered.
Before his imprisonment Doomra had taken a dread domain in the Shadowfell as his personal layer, & now it's become the resting place for his followers souls, where they become a unique type of fiends, that helps the cult.
Though the rest of the cults goal is to free him so that they may welcome an age of eat or be eaten, Zor'Tag's goal is simply to get his little boy back, because though they are both evil, he still greatly cares for his son.
Zor'Tag can only be killed by first destroying his 13 pseudo phylacteries, then killing him in his resting place with the Solar Spear to the heart.
Zor'Tag unlike other Dracoliches doesn't need to use other dead draconic skeletons to revive himself, instead he just respawns in his resting place much like a regular vampire does, & he doesn't need to sacrifice souls to keep his unlife in affect, but he does need to drink blood like a vampire/consume life force/psychic energy.
So yes he's hard to kill & he's very powerful, but he can be beaten, by a high enough level party, but beating him isn't the only thing to worry about because if the cult succeeds at freeing Doomra then he'll start working towards regaining his strength, & so at that point the party needs to find a way to lock him back up before he's fully restored his power.
The cult's symbol is a circle with 7 triangles poking out of the top, & 7 triangles poking out of the bottom all pointing inwards, with a tier drop in the center.
Source: r/DnDHomebrew · by /u/22ooo22xxxatg