I think a good arch villain should inspire some fear in the players. And it takes some work to establish that threat.
I use such an arch villain in my campaign. He is a god-like being from another world called Hydra, feasting on the souls of the dead. Throughout most of the campaign, I've build up the threat of the arch villain by simply mentioning him often, but never revealing him. The players got to experience his influence, and fight his minions, but they had no idea what he looked like, or if he could even be fought. Then one session my players did the unthinkable, they ventured into the realm of the dead, and got to see part of him. It left both the players and their characters pretty terrified, now that they knew what they were up against. "We can't fight this" was their first impression. Later on they started thinking about it, and figured "Maybe we can fight him indirectly, rather than directly".
Hydra
The arch villain in my current campaign is Hydra, a powerful Lovecraftian being that resides in the Eternal Depths. The Depths are a netherworld where the drowned and dead sailors go. The place is best described as an ice cold, pitch black, massive cavern of unparalleled size. The sky is a black rocky ceiling obscured by a blanket of thick fog, from which Hydra occasionally lowers one of its eldritch appendages. It would lower a massive trunk down to the ocean of souls below, and feast as a million souls cried out in horror. Hydra can invade the minds of mortals and speaks to them in their thoughts, as if speaking to a group of ants. It considers them pests... mere insects... lower beings, barely worthy of attention. Hydra has taken over the Depths from a local sea deity, the Lady of the Waves. Thus the souls of the dead cannot move on to the afterlife and are trapped in this realm, as food for Hydra. Hydra would also love to snack on the souls of mortals, but is not powerful enough to take on the established pantheon of gods that rule the mortal world. But his loyal servants open up a gateway for him to spread his influence, in the form of a dark cloud full of grasping hands, called the Harrowing. Hydra occasionally uses this gateway to send his fleet of living ships to the surface, which the players will soon face in an all out naval battle.
Hydra's minions all embody aquatic and cold themes, and are often twisted sea creatures, or corrupted servants. I make a strong distinction in my campaign between good sea creatures, and the twisted evil sea creature that serve Hydra. Hydra is sort of a horror from the deep, although I never make it clear in my campaign if the Eternal Depths where he resides, is another dimension, or simply a place deep beneath the sea.
I have plenty of minor villains as well, some of which are servants of Hydra. Currently the central lesser villains that the party have to deal with, is the Circle of Azarah; a group of evil wizard-outcasts that obey Hydra's will. They've already killed one of their members, but enough members remain, each with their own ship. I'm considering the option of maybe having one of the wizards betray the order at some point, if the players are able to persuate him to join their cause. It would be interesting to have not all of the villains be purely black hat.
The circle of Azarah
Grümwick Bristlethorn
Dresses in black with golden phases of the moon edged on his garments. His beard is black, like straw, and split into three long ends, which are tied three times. He carries a black cane with a golden ball at the top. Grümwick is a wizard with a limp, who works closely with Shamaneser Warpwood. He is mostly involved with augury and spying, and trying to get some magical eyes beyond the protective charms of notable buildings. Grümwick tends to spit and drool a bit when he talks, especially when angry. He loathes anyone that doesn’t use magic. And he has one magical wooden fake eye.
Sharokina Pitchwater
Also known as Sharokina the Merciless, and Sharokina the Cruel. An ex-Speaker of the Dead, who was banished for practicing necromancy on members of her own faction. Most notoriously was the crime of turning
Skua Hazeela Banefultouch (mother to an npc ally of the players) into her undead servant. As punishment she was stripped of her Skua title, half of her hair was cut, and she was banished from Witchclaw. Hazeela was of course laid to rest afterwards. Sharokina has a head that is permanently half bald (as punishment), and the other half has a long lock of black hair flowing down from it. One of her fingers is twisted, -the result of a magical duel with Hazeela. She wears black garments that resemble flowing seaweed, and she smells of a salty cold ocean breeze. It is said that she carries coldness with her when she enters a room. She enjoys making wands out of the fingers of her defeated foes, and one of her favorite wands was made from one of Hazeela’s fingers.
Shalmaneser Warpwood
The oldest wizard of the circle. Shalmaneser is a known devoted servant of Hydra, and an ex member of the Stoneoar. He was banished when his true allegiance became clear. This dwarven sorcerer was also a notable enemy of Beler the Builder. And by special decree, the ancient Stoneoar imbued their buildings with special glyphs that specifically banish Shamaneser from ever entering them.
Aram Seen, the Unseen
Master of illusions and teleportation. He wears a purple robe covered in the patterns of playing cards. He is a Kooghan wizard, dark of skin, with pale white hair, and hazel-colored eyes. Among the Kooghans, pale hair is considered a bad omen for any Kooghan child. It is seen as unnatural. And because people refused to look at him, he decided to become a specialist in the art of being unseen. Aram Seen is a tall strong wizard, his robes are decorated with a lot of gold. He carries a golden staff with a lantern that emits black smoke. He has a vertical scar across his forehead, down to his nose. A cut that was made when he was just a child, to purge the evil from his blood. Aram Seen is without a doubt the most mysterious of the circle, and his alignment leans more towards neutral rather than evil. The players may be able to turn him to their side.
Lady Kimura Yori
A Cyrian witch, known for her skills of deception, and magic potions. Lady Yori has beautiful Asian looks, but with pale white long hair, and she always wears a pale white kimono. White is the color of death in Cyrian culture. Yori is also known for her love for poisonous snakes. Yori was supposed to be dead after she was supposedly slain during a naval battle that the players took part in. But she is very much alive, and doesn’t seem to have any scars from her last ordeal at sea. She is a master of deception after all.
