Comments from the Finger: A long time ago, one of the first homebrew pieces I worked on for this blog was the Pathfinder Summoner class as a wizard tradition. The reason this has never seen the light of day is because it was rough around the edges in several ways, as it was both obtuse and not terribly true to the original class, but the mechanics I wrote for it were properly recycled. The 'design your own creature' bit was recycled for the Circle of the Unspeakable druid subclass, and some of the balancing mechanics for having a constant minion that wouldn't break the action economy ended up here.
Master of Shadow
You have undergone a terrifying rite of dark magic to become a member of the Secret Order of Shadowmasters, and have embraced the darkness in a way few ever will. As a result you have become pale and gaunt, and your shadow runs free. You can command it, and it will creep across the floor and ceilings for you like an extension of your very will.
Beginning at 3rd level, an insidious force from beyond the mortal realm has freed your shadow from the confines of your body, and it can now move independently. Your shadow acts on your turn, though it doesn't take actions unless you command it to. It has a base speed equal to twice yours and has the same size as you, though it has 0 for each ability score. Your shadow can never move more than 100 feet from you.
Your shadow occupies the same area of floor that a medium creature would, though it can occupy the same spot as another creature or object. It has an armor class of 10, and vanishes when it takes any damage. Your shadow reappears at your heels at the beginning of your turn the round after it takes damage. Your shadow vanishes if it enters an area of light created by a spell of 3rd level or higher, and cannot reappear while you are in such an area. If you shadow enters a heavily obscured area or one of magical darkness, it is effectively invisible.
Your shadow can appear to be the shadow of other creatures and act convincingly using your Charisma (Performance) or Charisma (Deception) skill.
Finally, your shadow has the ability to cast chill touch at your level using an attack modifier equal to your proficiency bonus + you Charisma modifier. You can command it to do so as a bonus action. Additionally, you shadow can move small items weighing no more than 5 pounds across the floor provided they are not being held or carried.
At 3rd level, now that you are without your shadow, you can see normally in darkness, both magical and nonmagical, to a distance of 120 feet. In contrast, your shadow has no senses, and can only perceive that which you do.
By 9th level, you can command your shadow to cast darkness on itself as a bonus action. Shadows of the damned crowd the darkness and hinder movement, making the area difficult terrain. At 13th level, the area in darkness is unnaturally silent and becomes an area of magical silence. You shadow maintains concentration on this spell until it vanishes. After it uses this ability, it cannot do so again until you complete a short or long rest.
At 13th level, as a reaction when an attack is made against you or a spell affects you, you can flicker out of existence. You teleport to your shadow, up to 30 feet. Roll a d20. On an 11 or higher, the attack or spell does not affect you. Otherwise, you take half damage from the attack or spell (and suffer all other effects of the attack or spell normally) before you teleport. After you use this ability, you must finish a short or long rest before using it again.
Beginning at 17th level, once per day for 1 minute, your shadow can take on physical form composed of shadowstuff. It becomes a medium creature, can perform any action you can except for casting spells, and has the same ability scores, saving throws, and nonmagical equipment you have but only one fourth the total hit points, rounded down. While your shadow has physical form, it only vanishes if it is reduced to 0 hit points.
Changelog: 8/4/15: Flicker reworded. Shadowclone specifies that your shadow possesses your nonmagical equipment when it takes on physical form.
Flicker now takes half damage on a failed roll, rather than all.
Release Shadow: Your shadow is invisible in darkness, rather than considered to occupy the entire region.
9/16/15: Shadow no longer counts as an ally for the purposes of Sneak Attack (more of a trial change until we can playtest)
12/4/15: Release Shadow: Your shadow can act as the shadow of another creature with Deception or Performance.
12/16/16: Umbral Silence: Reworded to specify the darkness is difficult terrain