Voidspawn
Voidspawn are spawned from the death of dimensions as there remains fester in the Void. As such, no two are the same. Each time one was created, at least one undecillion different variables are rolled in the random design process. Sometimes common traits bubble to the surface, but most are wildly different in appearance and nature. Voidspawn know nothing but the instinct to amass power and evolve through any means necessary. They do this by hunting each other and feasting on the left over energy of other dimensions that was discharged into the Void.
Growth #
Voidspawn grew by consuming the energy of dimensions. They took the information gathered from them and adapted to their environments at an alarming rate. Most Voidspawn accomplished this by joining the free-for-all for the leftover energy of dimensions that had 'voided', or perished and been discharged into the Void. This survival of the fittest was a chaotic and dangerous mess.
Some Voidspawn were much smarter however. If a Voidspawn infiltrated a live dimension it could feast on its energies from the inside. Since there were requirements to do so, there was less competition for those that did. As they ate, they thinned the dimension's null film in the process. If they were left alone to consume as much as they wanted, a Voidspawn would eventually completely destroy the null film and the entire dimension would be voided.
Regeneration #
Voidspawn only died when their essence was destroyed with the power of the Void. The Void continuously regenerated their bodies upon destruction. For a Voidborn or Voidspawn this was not an issue, but this made them fearsome opponents to dimension dwellers. Unless one could destroy them with the aid of supernatural power or twist their dimension's null film, there was no way to get rid of them.
While a Voidspawn was regenerating it could not continue to sap a dimension of its strength, however. This meant that the natives of dimensions with Voidspawn could indefinitely hold them at bay by repeatedly destroying them as they rose again. Since the regeneration process took a significant amount of time to complete this event needed only to occur periodically. That would require a consistently coordinated effort, however, which was difficult to keep up forever. A Voidspawn need do nothing but wait for kingdoms to rise and fall... and for knowledge to be lost.
Power #
A Voidspawn's ceaseless adaptation to the contents of other dimensions meant they could display any variation of abilities. They typically gained abilities that used to be native to the dimensional energy they feasted on, but they could also use the energy to adapt to harmful effects in their environment. Some even then gained abilities that could replicate effects from phenomena within the void that they had witnessed, meaning Voidspawn could inadvertently teach each other their adaptations.
Voidspawn were natural fonts of Void energy. If the laws of a dimension they visited failed to provide them with the resources to use their adaptations, they could still fuel them with the power they generated themselves.
Death #
These creatures of chaos though fearsome and powerful they had been, could not escape the throes of death. Over the course of its life, a Voidspawn inexplicably lost its ability to contain its power within its form. Once it grew too old, its body would melt back into the energies it had consumed over its lifetime, returning to the Void from whence it came. This was known as "succumbing".