Class - The Abyss Mystic

2 And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.

3 And God said, Let there be light: and there was light.

We live in a world of light, form, stability, reality. Everything the light falls upon is defined. Pinned into place by the act of witnessing it.
It was not always this way. Before the creation of light chained the world into its current form, darkness reigned. Things were imprecise, mutable, filled with potential. Far from being empty, there were intelligences in the dark, beings of the abyss. The world was a constantly-shifting quantum foam, and these creatures shaped it to their whim.
Such true darkness is rare in our current world. Mere night-time is still touched by the faint light of the moon and stars. To escape the light entirely, one must travel into the depths of the ocean, into the lowest points of the oldest dungeons, into the deepest veins of the earth. One must descend into the abyss. Here, the world is truly lightless. Here, free from the restrictions of vision and reality, one can commune with the true darkness that predated creation.

Few mortals have any clue as to the potential held in the darkness. To turn away from the light, to willingly blind oneself and immerse oneself in the void is seemingly insane. There are a few, though, who know what is possible. Who study the true black arts. Who draw upon the darkness and channel its power.
Such individuals are frequently found in the company of adventuring parties, hoping to be taken into the earth's depths, to encounter the true darkness that can be found down there.

Hit Dice: d4
Saves: As a Magic User
Attacks: As a Thief
XP: As a Magic User
Equipment Restrictions: As a Thief
Alignment: Must be Chaotic

Darksight: In absolute darkness (including supernatural darkness), an Abyss Mystic can navigate as easily as broad daylight. This ability does not grant any ability to see better in low-light conditions. Even very dim light ruins darksight, leaving the Abyss Mystic groping about in the gloom like anybody else.
Veins of the Earth says magic darkvision doesn't really work in the veins. This stuff explicitly does; the darkness of the veins is an asset to an abyss mystic, not an impediment.
Channel The Abyss: By vomiting forth the shadows within themselves, an Abyss Mystic can create a pool of absolute darkness in a 10 foot radius around them. Doing so costs the Abyss Mystic 1 HP as they draw out the darkness inside them. This pool of darkness follows the mystic if they move, and lasts until they sleep or choose to dismiss it.

Abyss Mysticism: In absolute darkness, an Abyss Mystic can invoke the darkness from before creation to create supernatural effects, equivalent to the spells used by other classes.
To do this, they choose which spell they wish to cast, and roll a casting dice, which is normally a d20. If the result is their level, or less, the spell is successfully cast.
For each round spent gathering abyssal power before casting, reduce the size of the casting dice by 1 step (from a d20 to a d12, then d10, d8, d6 and finally d4).
If the maximum result on the casting dice is rolled (IE a 20 on a d20, a 12 on a d12, etc), then the spell automatically fails, and the mystic's form begins to dissolve into primordial darkness. They take as much damage as their maximum HP total. Roll the casting dice again, and reduce the damage taken by that much.
Example:
 A 3rd level Abyss Mystic with 9 HP wishes to cast Silence. There is no absolute darkness nearby, so they must create some using Channel the Abyss (taking 1 damage in the process, reducing them to 8 HP). They then spend two rounds gathering power, reducing their casting dice from a d20 to a d10. On the third round, they attempt to cast the spell, rolling a d10. 
If the result is 1-3 (their level or less), the spell is cast successfully.
If the result is 4-9, the spell fails but nothing bad happens.
If the result is 10 (the maximum possible), they begin to dissolve into shadow. They take 9 (their maximum hp) minus d10 (the casting dice) damage.

At first level, they know only a single spell of the Abyss. At each level, they learn another spell, either randomly chosen or of the Abyss Mystic's choice, depending on how the game you're running handles it. Abyssal spells don't use spell ranks; count them all as 1st level spells for any effect that cares.

Abyssal Spells:

1. Abyssal Tar. Duration 1 round/level. Radius 30 feet. This spell causes the darkness to become almost tangible, slowing and constraining those within it. Any creatures within the spell's radius in absolute darkness move at half speed, and are only able to attack, cast spells or take other such dramatic actions every other round (as if affected by a Slow spell). Those in deep shadow, but not absolute darkness, get to make a Save vs Paralysis to resist the spell's effect each round. Creatures immune to darkness, such as Abyss Mystics, are immune.
2. Arms of the Abyss.. Duration 1 round/level. Range 20 feet. This spell creates a semi-tangible black tendril that emerges from an area of shadow or darkness that the mystic can see. The arm can extend out to ten feet in length, and can manipulate objects with as much dexterity as a human hand. If issued a command by the mystic, the arm obeys, otherwise it will lash out blindly at its surroundings. It can attack (as a 1-hd monster), dealing d4 damage on a hit, or else grapple, snatch items, etc like any other creature. It has as many HP as the mystic's level. Exposure to light is harmful to the arm; it takes 1 damage a round if exposed to any light at all, while brighter light (such as torchlight) deals d4 damage a round, and full daylight does d12 a round.
3. Charm Shades. This spell functions exactly like the spell Charm Person, except that it only effects non-physical undead or extra-planar creatures such as ghosts, invisible stalkers and so forth. Shadows, Shades and other monsters explicitly made of shadow or darkness get no save to resist the spell. Exposing the subject to bright light ends the spell immediately.
4. Control Shadows. Duration 1 round/level. Radius 30 feet. During the spell's duration, the mystic controls the shape, movement, depth and extent of all shadows within the effect's radius (which might extend outside the pool of absolute darkness created by the mystic). They can create shadows of things that aren't there, create enough shadow for team-mates to hide in, extend pools of shadow over an enemy's eyes to blind them, or create shadows that another of the mystic's spells can make use of.
5. Create Sensations. Duration 1 round/level. Radius 30 feet. During the spell's duration, the Mystic can create illusory sensations for any sense except vision. They can create tactile sensations, noises, smells, tastes, and even spoof unusual senses possessed by creatures (such as a shark's ability to detect electrical charge). The sensations can be tailored so different victims experience different things. There is no save initially, but a Save vs Magic is allowed when a victim has evidence that the sensation might be false, allowing them to tell for sure that it's only an illusion.
6. Dissolve into Darkness. Duration 1 round/level. During the spell's duration, the mystic's physical form evaporates, leaving only a two-dimensional shadow behind. Equipment carried by the mystic is likewise transformed. Whilst two-dimensional in this way, the mystic cannot be physically touched or touch things, and is immune to most attacks. They can move only slowly - 10 feet per round - as their form slithers across whichever surface it's projected onto. When not hidden in darkness or shadow, exposure to dim light deals 1 damage to them per round, exposure to brighter light (such as torchlight) deals d4 damage per round, and sunlight or equivalent does d12 damage per round. The mystic can still cast other abyssal spells in this form.
7. Enlarge/Shrink. (as the existing spell).
8. Extinguish. Range 20 feet. This spell completely extinguishes a single fire or light source within range. 
9. Eyes of the Abyss. Duration 1 round/level. Radius 30 feet. During the spell's duration, the mystic can see (and hear, touch, smell etc) everything that happens in any absolute darkness in the spell's radius, granting them a sort of limited-radius omniscience. The spell allows them to see through illusions, invisibility, etc within the spell's area of effect. 
10. Feather Fall (as the existing spell)
11. Peer Through The Abyss.. Duration 1 round/level. This spell functions exactly like the spell Clairvoyance, except that when used the mystic can only perceive things in absolute darkness. Anything in even very slight light cannot be viewed by the spell.
12. Reach Through Shadows. Duration 1 round/level. Radius 30 feet. During this spell's duration, the mystic can reach their hand into the darkness surrounding them, and have it emerge from any shadow or darkness in range, up to the shoulder. Anything they grab can be pulled back to the mystic, or they can use the spell to place things away from them.
13. Sever Shadow.. Range 20 feet. The mystic can extend a knife of shadow from the darkness they lurk in, attacking the shadow of an enemy nearby. As the enemy's shadow is ripped apart, corresponding wounds appear on their body. The victim must be illuminated enough to cast a distinct shadow, which must fall within the spell's 20 foot range. The shadow-knife hits automatically, dealing d6 damage plus the Mystic's level.
14. Shroud.. Duration 1 turn/level. The mystic pulls a shroud of shadow over their allies, concealing them. The spell's subject (who must be within the mystic's pool of darkness when the spell is cast) gains the Hide In Shadows ability of a Thief, of the mystic's level. If the subject is already a thief (or otherwise has this ability), then add the mystic's level to their own for the purposes of their chance at hiding.
15. Silence (as the existing spell)
16. Step Through Shadows.. Range line-of-sight. The mystic steps into the darkness, and emerges from any area of shadow or darkness they can see that is large enough to fit their whole body into.
17. Spider Climb (as the existing spell)
18. Undo The Chains of Light. Duration 1 round/level. Radius 30 feet. This spell causes things to revert to the state they were in before light and space gave things solid, tangible existence, dissolving into their dark, primordial potential. Everything and everybody within the spell's radius is affected. Objects slowly degrade over time, crumbling to black dust, and then dissolving into raw darkness, although this will take hours to complete. Creatures are more vulnerable; it only takes a little disruption for the orrder that makes life possible to be disrupted. A creature in sunlight or similar light is unaffected. A creature in bright light (such as torchlight) takes 1 damage a round, a creature in dim light takes d4 damage a round, and a creature in absolute darkness takes d12 damage a round. Creatures immune to darkness (such as Abyss Mystics) are unaffected.
19. Unseen Servant (as the existing spell)
20. Water Breathing (as the existing spell)