Editing Setting:Planescape Improvement Project (section)

===Biology of Outsiders===
{{Main|Outsider}}
I have come up with some new ideas for the biology of creatures of the outer planes. Creatures of the outer planes are physical souls. Even though they have biology similar to material creatures, their bodies are actually made of spiritual matter that closely imitates organic matter. One of the consequences of being physical souls is that creatures of the outer planes cannot reproduce without sacrificing some of their power because entirely new souls can only come into existence in material matter. But they can get around this by breeding with a material being, which requires the outsider to sacrifice only a tiny fraction of the power they would if reproducing alone or with another outsider partner. Because of this, most outsiders are formed from the souls of the dead instead of being naturally born, as turning souls into more of their kind comes at far less cost.

When a soul arrives on the outer planes, there are two possible forms that they may immediately take. Most souls fail to retain memories of their previous life and end up as soul larvae, a helpless and nearly mindless form. Larvae are easily converted into the lowest rank of the native outsiders of that plane. On good-aligned planes, larvae are converted as soon as they are found by a good outsider capable of promoting them because of their vulnerability. Petitioners are the souls of people who manage to retain their identity after arriving on the outer planes. Petitioners usually retain the same shape they did in life but are not always recognizable. Petitioners may keep some of the abilities they had in life but usually are far weaker than they originally were. A fighter petitioner will go down much more quickly than they did in life, and a wizard petitioner will still be able to cast high-level spells but will only be able to cast one or two spells per day. Petitioners are more difficult to promote or demote into the form of a native outsider than larvae, and if changed, will lose the abilities they had in life. Powerful creatures like dragons can also become petitioners and larvae but