Outsiders are at least partially composed of the essence of a plane other then the Prime Plane. Many outsiders have darkvision out to sixty feet. As a group, they have no other special abilities or immunities.
Outsider Death & Rebirth In planescape and 2nd ed. game, outsiders are not necessarily destroyed permanently when killed. Some are able to reform themselves in their home planes. The following serves to update those phenomena to v3.5.
Devil (Baatezu) A baatezu reforms in the Nine Hells if killed off-plane after having left the Nine Hells out of its own free will. This includes obeying the commands of a superior. Summoned or otherwise removed baatezu always reform. Such baatezu reforms as a nupperibo and does not regain its full memory until it reaches its former station. The nupperibo must then be reduced to a lemure before moving up the ranks. It usually takes 4d% years before such a nupperibo is found. (Some subordinates prefer their commanders to remain missing.) The time taken for it to be reinstated back to its full station varies, but most are reinstated in 3d20 years per HD. A baatezu killed in the Nine Hells is permanently dead. The reform ability applies only to baatezu and not all devils.
Demon (Tanar’ri) Any tanar’ri killed in the Abyss is permanently dead, but it is rumored that some tanar’ri carry pieces of the Abyss in their hearts. A tanar’ri reforms in the Abyss if it is killed off-plane and if it has at least 10 racial HD. The reformation takes 5d20+60 years. During this time, the tanar’ri is considered dead and cannot be affected or contacted in any way except by true resurrection and like effects. At the end of the reformation, it must make a DC20 will save or be completely absorbed by the Abyss. Otherwise, it reforms, pulling itself out of the plane. If the will save result equals to at least CR+15, it may choose a new form which is 1 CR higher than its old form. The reform ability applies only to tanar’ri and not all demons.
For example, 3 glabrezu (12 HD, CR13, will +11) died in a Blood War skirmish in the Gray Waste. Their spirits reform in the Abyss after 65+ years. The demons attempt their will saves. The first glabrezu saves at 15 (1d20 roll=4) and is absorbed into the Abyss. The second glabrezu saves at 21 (1d20 roll=10) and reforms as a normal glabrezu. The third glabrezu saves at 29 (1d20 roll=18) and may become a CR14 demon, either a nalfeshnee or a glabrezu advanced by 2 HD.
Yugoloth Most yugoloths are permanently dead when killed. However, a yugoloth with at least 12 racial HD reforms back on its home plane in 1d4+9 years if killed on any plane other than Gehenna, Carceri or Hades. During this time, the yugoloth is considered dead and cannot be affected or contacted in any way except by true resurrection and like effects. A specific yugoloth’s home plane is the plane from which it was originally formed, usually Gehenna, Carceri or Hades.
Two yugoloths deviate from this rule. Arcanaloths can be permanently destroyed specifically in Gehenna only. Such arcanaloths yield their knowledge into the racial memory of all arcanaloths. The dergholoth reforms in 2d6 days, regardless of its racial HD, if it is killed in any plane which is not evil-aligned.
Demodand (Gehreleth) Unlike other fiends, a demodand has no reform ability. However, the number of demodands is said to be fixed by Apomps. Thus, if a farastu dies, another one rises in Carceri to take its place.
Eladrin When an eladrin dies outside of Arborea, it reforms in Arborea just like tanar’ri demons reform in the Abyss. When an eladrin dies in Arborea, it is permanently dead and the pain (and glory, in some cases) of the death can be felt by all who knew the eladrin, regardless of the intervening distance. This feeling is a sudden awareness and a sense of loss. A DC 20 Wisdom check can identify the eladrin. Rumors claim that if other eladrins can also identify the slayer simply by looking into the latter’s eyes.
In certain prime material worlds where direct divine and outsider interventions are restricted, eladrins are required to manifest a veil. The eladrin must take on a guise common to that world, usually a human or elf and commonly a wandering bard. The Veil restricts the eladrin to act within the capabilities of its assumed guise whenever a native might be near to see. If the eladrin violates the Veil, it must return to and remain in Arborea for 1,001 years before being allowed to roam the prime material worlds again. Usually, the violator eladrin is allowed 3d20 minutes to attend to any unfinished business before its planar departure.
Modron When a modron dies, regardless of the location of death, its essence returns to Mechanus. The individual modron (if modrons can be said to have individuality) is dead, but a monodron is created to replace the dead unit. If the dead unit was of a higher rank, a modron from 1 rank lower is instantly promoted to replace the dead unit. The promotion continues until the new monodron steps into the hierarchy.
Other Exemplars Nothing is known about the rebirth or reformation nature of other exemplars like archons or slaad. It is likely that they do not possess such abilities or they may take on the reformation nature of their counterparts, e.g. perhaps archons reform in a similar way as the baatezu.