Despite the fact that Doppel is very much a defective incubus by all definitions, he's still able to shapeshift to a slight degree to make himself look less like a neon blue blob and more like an actual person with real facial features and hair and stuff. Initially Jared thought this would be super helpful because hey, who wouldn't want a doppelgänger to do your work while you screw off elsewhere? Of course, when he realized that Doppel's copying skills are....limited at best, to say the least, he kind of gave up on the idea entirely.

So now Doppel just randomly assumes a shitty version of Jared's form for fun and profit(?) Too bad his shapeshifting really doesn't work neck down.