A translucent humanoid stands before you, looking like a mix between a tall human and a Mistwraith. Its jelly like flesh can be seen constantly shifting, new muscles being made and unmade as you watch, the only constant is the shape and the dozens of metal spikes stuck haphazardly through its form. Worst of all is its face, which shifts between many different people, eventually you find yourself staring at your own perfect, jelly-like reflection...
Decades, perhaps centuries ago, a Hemalurgist tried to grant sentience and intelligence to a Mistwraith. He succeeded, though the creature was not what anyone would call smart. Over the years he gave it a few more Hemalurgic spikes, granting a few allomantic or feruchemic powers, and trying to augment its learning capability.
After its master died, the creature wandered on its own, knowing only that its master kept driving stakes into it to grant it "Gifts" from others. Surely then it should keep doing the same? Surely its master had a plan at the end for all the pain?
And so the creature hunted, occasionally carrying off Skaa in the night, even sometimes a wandering Noble who braved the mists outside a lonely plantation.
Each victim is dragged off and eventually staked through the heart, the stake then being rammed into the Creature's own flesh. Sometimes doing nothing, sometimes granting new allomantic or feruchemic abilities.
Slowly the creature raises its hand, holding a huge steel spike as long as your forearm. "Master granted gifts like this, now we take gifts like he wanted". With blinding speed the creature suddenly shoots forward grabbing your arm and twisting it behind your back, holding you immobile. It reaches past you and you feel a cold point in your back, like the tip of a nail. "Will you give a gift as well?"
With a sudden flare of pain you feel something puncture your back, your ribs snapping as it drives all the way through your body and out the front. The creature keeps pushing, driving the stake entirely through your body and into its own. As pain overwhelms you and your consciousness fades, all you can do is stare into its eyes, your eyes, as something familiar grows behind them. "Your gift is sweet..."
The Creature can have any combination of allomantic and feruchemic abilities, as well as all the strengths and resiliences of a Mistwraith.