A process by which powerful beings from other planes can create a physical form in Aserra's Prime Material Plane. This primarily applies to gods and dragons, but also demons and angels occasionally make use of the practice. Decension, the opposite of ascension is also a suitable term.
These entities exist on higher planes, and as such, cannot transfer matter from theirs to the material plane. Instead, the process of transubstantiation uses matter to create a physical body with which they can interact with. Energies, such as mana, can cross planes, allowing for the manipulation of physical elements. This body can take any form they wish, but most frequently Aserra's gods will use this technique to create a replica of their true body (sans wings) so that people will see them for who they are. This form can be only animated materials that look passable enough, but the more adept can create a fully organic body capable of all normal functions, though they have the power to manipulate that body beyond natural limits (go without eating or sleeping, healing wounds, halting deterioration, etc.).
Dragons populated Aserra's material plane using this technique. The original mortal dragons transubstantiated their forms into the mortal world, fully organic and functional. Those original dragons reproduced, and their descendants now exist on the Prime Material Plane, though they are significantly less powerful than their extra-planar kin.