Devils are lawful evil outsiders that hail from the plane of Hell.
Devils possess a particular suite of traits (unless otherwise noted in a creature's entry).
Source: Ultimate Magic (see Binding Outsiders for further details.)
Devils regard both holy items and silver as deadly substances, and instinctively shy away from contact with such items. Even those for whom silver presents no danger avoid its touch whenever possible. Binders who want to deal with infernal outsiders as putative allies keep these substances at least 60 feet from the summoning circle; however, if they wish to threaten their infernal subjects, they keep them close at hand. The powdered silver used to create the magic circle is a warning and a trap, but it is not an overt threat—summoned devils recognize it as part of the procedure to call them to the Material Plane. Note that even silver candlesticks or bells can be used as weapons of opportunity, but the best defense, should the wizard choose to display force, is a weapon bonded with alchemical silver.
An even better defense against devils, however, is a holy weapon. As with demons, a holy weapon is strong enough to drive through any devil’s natural defenses, and the presence of such an item in the summoning chamber is an affront to more powerful or subtle devils.
Note that all devils are immune to fire and poison; the blasted landscapes of their home plane quickly destroy any who show vulnerabilities to these effects. All devils can withstand acid and cold as well, though to varying degrees, and few of them show any fear of suffering that damage. They have resistance to acid 10 and cold 10. Additionally, one can enhance summoning for specific kinds of devils by appealing to those devils’ specific natures.
Accuser Devil: Popular among conjurers and summoners as spies and infiltrators, accuser devils often forgo haggling on gifts for their services, as the information they gain is worth more than any gift of treasure the binder can offer.
Barbed Devil (SR 22): Extraordinarily jealous of their duties and even more so of their time, barbed devils may grudgingly accept offers of rare treasures and gems worth more than 2,000 gp, with the usual +2 Charisma bonus to summoning—but only when the task takes less than 24 hours to complete. If the service takes any longer, the binder takes a –2 Charisma penalty.
Bearded Devil (SR 16): The best way to attract the eye of a bearded devil is to offer a restrained victim for its bloody use, so that it might painfully murder its target.
Belier Devil (SR 28): These massive masterminds are rarely summoned to the Material Plane, but when they are, they often try to finagle their way out of such circumstances as quickly as possible.
Erinyes (SR 19): As the spirits of corrupted angels, erinyes are bitter and rage against the heavens. To entice an erinyes, offer it a significant holy item for it to despoil, or the cleric of a good-aligned god to ravish and ruin.
Handmaiden Devil (SR 25): Deals made with handmaiden devils are often extremely hard bargains. They typically ask for the unthinkable, such as the lives of innocent children—the younger the better.
Horned Devil (SR 27): As the elite of Hell’s armies, horned devils value strength and daunting power; anyone who offers them an intimidating weapon enchanted to +2 or better gains the +2 Charisma bonus.
Ice Devil (SR 24): As the schemers and planners of Hell’s devils, laboring in their personal machinations, gelugons are extraordinarily difficult to summon. However, casters willing to offer an exchange of services—one in which the caster is likely to see the short end of the deal—may earn a Charisma bonus. Those who renege on their bargains with gelugons often learn what it means to displease Hell.
Immolation Devil (SR 30): These devils often ask for lands on the Material Plane as gifts. If such lands are granted, they use these places to launch attacks on neighbors, further expanding the territory of Hell.
Lemure: Lemures prefer reminders of their former lives, and so the best offering is food or pornography.
Pit Fiend (SR 31): Pit fiends, the greatest of all the non-noble devils in Hell, are rarely tempted to answer a summons; when called, most of them come to see the stupidity or the arrogance that brought them to the Material Plane before snatching the wizard away for an eternity of torment. Only the greatest of promises, such as a noble offering the enslavement of an entire empire, a priest offering the destruction of holy relics, or an antipaladin pledging the delivery of a helpless and noteworthy angel for the pit fiend’s pleasure, might induce the pit fiend into service.
Masters of corruption and despoilers of purity, devils seek to destroy all things good and drag mortal souls back with them to the depths of Hell.
As the most numerous fiendish occupants of Hell, the various forms of devils are well catalogued by diabolists. Most are known by two names: an evocative title given to the fiends by commoners and folklore, and an obscure, ancient designation spoken by the servants of Hell and those who would seek to deal with the damned.
Born from the foulest of mortal souls—their personalities and memories long since scoured by millennia of torment—would-be devils rise from the masses of suffering souls as lemures, revolting beings of mindless evil potentiality. Only through continued centuries of torture or by the edicts of more powerful devils do these least of devilkind rise to become deadlier fiends, graduating through a pain-wracked metamorphosis dictated by their masters or the infernal whims of Hell's semi-sentient layers. While fiendish lords wield transformation into greater or lesser forms as both prize and punishment, some devils spontaneously rise from particularly evil souls long trapped upon an infernal layer. Thus, although the various diabolical breeds possess recognizable abilities and hold generalized rankings in the great infernal hierarchy, a devil's type alone does not always correspond to a specific tenure of torment or place in the infernal chain of command.
Devils fill the nine layers of Hell, though certain fiends are more common on specific layers than others, their specialized duties or fealty to individual archdevils drawing them to one torturous domain more than others. Although the various types of devils tend to specialize in unique forms of depravity or temptation, the hierarchies of Hell are not without flexibility for uncommon individual talents. Thus, particularly watchful hamatulas might join the ranks of Phlegethon's bone devil inquisitors, while veteran barbazus might serve among the pit fiends of Nessus.
Beyond the pits of Hell, devils often travel to the Material Plane at the summons of evil spellcasters. Quick to bargain and willing to serve mortals to assure their damnation, devils ever obey the letter of their agreements, but serve the whims of Hell foremost. Thus, even the least of devilkind might come to the Material Plane intent on further corrupting souls, cleverly escaping the bonds of their contracts to indulge their own plots, or to further the unspeakable goals of the archdevils of Hell.
Diabolists speak often of the rankings of Hell, the distinctions made between devils that distinguish the foot soldiers from the commanders of Hell's armies. While such divisions mean little to most mortals—a devil being a deadly foe in any incarnation—the hierarchies and nuances of Hell's society carry distinctions vital to the survival of any who would commune with devils. What distinguishes a breed of devils above or below others is more than a matter of brawn, with several cunning types of fiend holding priority over their fundamentally stronger brethren. While a devil's station does not mean it can instantly command every other devil of inferior standing, it does imply which fiends might serve their brethren or hold influence over others.
Below these are the devil races themselves, from the lordly and malevolent pit fiends all the way down to the lowly, malformed lemure.
Listed here, from the absolute weakest devils to the lords of Hell, is the most basic hierarchy of the infernal realm's best-known denizens.
Least Devils: imps, lemures
Lesser Devils: bearded devils (barbazus), erinyes, barbed devils (hamatulas), bone devils (osyluths)
Greater Devils: horned devils (cornugons), ice devils (gelugons), pit fiends