Doppelgangers must be created, not born.
The most notable (and so far only) doppelgangers encountered in the Quest are Doosh .
Relation to OriginalEdit
Doppelgangers are basically clones of any specific living being, the "Original" However, many of their dominant and minor characteristics are completely the opposite of the original; ex if an Original is quick-tempered and likes sour food, then the doppelganger will be patient and have a sweet tooth.
Contrary to Doosh's portrayal, doppelgangers by their nature are not evil. A doppelganger's nature reflects that of his/her Original; if the Original is generally good-natured, then the doppelganger will be generally bad natured. Thus, if any of the stories villains were to have an Opposite created for them, it would be a hero. Since many people (including some Smoosh members) are generally in a "gray area" of morality, so will doppelgangers, since the Opposite of the middle, is also the middle.
As a dynamic and changing reflection of a certain persons soul, their nature and existence is dependent on that of their Original. If the Original dies, then so will the doppelganger. Their nature will also change if the Original's does: if for example an Original goes from being Lawful to Anarchist, then the Doppelganger will naturally go from Anarchist to Lawful.
Technically, doppelgangers are not "true souls" since they are just "living mirrors" of sorts; thus when they die they...well, you'll find that out later.
It should be noted that some time after their creation, doppelgangers develop their own personality that is independent (and not "opposite") of the Original. Sometimes a doppelganger will even develop a trait that is equal to their Originals; but this is very rare.