This creature superficially resembles its tribesfolk, though its posture is hunched and features exaggerated. Most possess exaggerated claws and fangs, their scales twisted and nobby from an overabundance of mana. Their intelligence is merciless and cunning.
Despite their appearance, the Forgotten are a tragic creature. There are two ways the Forgotten may form. The first is through their own desperation; not every sith-makar Awakened and (even some who had) seek to strengthen their own draconic ties at any cost. To do so, they begin eating the flesh of their kin. Over time, the excess of energies warps them and flesh becomes the one thing they hunger for.
The second is through Charneth deliberation. Charn discovered this property by accident, but were quick to turn it to their advantage. They begin by capturing sith-makar young of any age. These sith-makar are then tortured to confuse and enmadden them. From there, they are strapped and force-fed a diet of their own kin until the magic takes effect. These Forgotten are particularly ferocious and deadly. Charn straps claws and armor to their form if they grow none, ensuring these "shock troops" survive as long as possible while rending devastation.
There is no known way to reverse the process.
Mechanically, the Forgotten are sith-makar with the Vast-wrought template added, and barbarian level(s), so may be adjusted for challenge. Feel free to give them claws, or a claw and a set of fangs as suits you. The bile breathweapon is from mana melting their insides from the inside-out. Maybe they have a partially working 'other' breathweapon. Give them nonworking stub-wings, or even half of a wing at an angle from a catastrophically failed transformation into half-dragon, and so on.
For inspiration, imagine the Reavers from Firefly, or Deathguards from Beastmaster. They aren't meant to be PCs; a creature having gone fully through the process would be unplayable.
CE Medium Monstrous Humanoid (Abberation sith-makar)
Init 1; Senses Darkvision 60', low-light vision
AC 17 (+4 natural, +4 Hide armor, +1 dex, -2 rage)
HP 46 (4d12+20)
Fort +6 (8 when raging), Ref +2, Will +3 (5 when raging, additional +4 versus mind-affecting)
Special Qualities Uncanny Dodge, Trap Sense +1, Resist Fire 5, immune to sleep effects, paralysis effects, disease and poison. DR 5/cold iron, and SR 16.
Speed 30 feet
Melee +9 d4+5 bite and 2 claws at +9 d6+5
Space 5' Reach 5'
Special Rage, Breath Weapon
Str 16 (20), Dex 12, Con 16 (20), Int 6, Wis 11, Cha 12
Feats: Razortusk, Run or Keen Scent
Rage Powers: Lesser Beast Totem, Knockdown
Skills: Survival: 2 (+5), Intimidate: 4 (+8), Perception: 1 (+5), Climb 1 (+7 or 9)
Tactics: At the sight of prey, the Forgotten becomes single-minded and cannot be dissuaded. They retain limited cunning, however, so may also pursue prey or attempt to ambush them using terrain. They rage immediately when fighting. When found in packs, one will attempt to trip using Knockdown, with packmates swarming the fallen creature. While they prefer the flesh of sith-makar over other humanoids, they will consume both.
Breath Weapon (Ex): A Forgotten creature can spray a 30-foot cone of acidic bile from its mouth as a standard action once every 1d4 rounds. The acid damage caused by this attack at CR5 is 2d6. A successful Reflex save (DC 16, or 10 + 1/2 Forgotten's HD + the Forgotten's Constitution modifier) halves any damage taken from this attack. Feel free to change the damage type to reflect a mockery of their ancestry.
Shattered Mind (deformity): The mutant takes a –2 penalty to Intelligence, but gains a +2 racial bonus on Will saves.
Uncanny Dodge: As barbarian ability.
Rage: As 4th level barbarian.
Spell resistance increases to 11 + its adjusted CR. DR increases to DR 10/cold iron if the base creature has 11 HD or more. Breathweapon increases to 1d6/2 hit dice.