A demonologist is a mortal who has devoted his life to the study of fiends; despite the name, he may be equally skilled dealing with devils, yugoloths, and other outsiders native to the lower planes. He is practiced in dealing with them, fighting them, and using them for his own gain. He even gains some fiendish abilities due to his studies and devotion to the creatures of the lower planes. Demonologists are always evil, although they might not think of themselves as such. No character can get so close to the mind of utter corruption and come away unchanged.
Most demonologists were once wizards or sorcerers, although bards who delve into evil lore also frequently meet the requirements of the class.
Alignment: Any Evil
Spellcasting: Able to cast 3rd-level arcane spells
Skills: Lore 8 ranks
Feats: Augment Summoning
Class Features Edit
Hit Die: d4
Base Attack Bonus: Low
High Saves: Will
Skill Points: 4 + Int modifier
Class Skills: Concentration, Craft Alchemy, Intimidate, Lore, and Spellcraft
Arcane Spellcasting: At each level except 3rd, 6th, and 9th, demonologists gain new spells per day and an added level of effective spellcasting in whatever arcane spellcasting class gave them access to 3rd-level arcane spells when becoming a demonologist. If a character has multiple classes that give him access to 3rd-level arcane spells, he must choose which spellcasting class will benefit from demonologist levels when first selecting this prestige class.
Fortification Versus Fiends: A 2nd-level demonologist learns extensive lore to protect himself against the fiends he would summon and control. Against outsiders, he gains a +2 bonus to AC and a +2 bonus to saves versus spells.
Summoning Mastery: When a demonologist of 3rd level or higher casts a summon monster spell, it is empowered beyond what Augment Summoning provides, gaining two outsider levels and a +1 unholy bonus to its attacks.
Note: (A demonologist with the corpse crafter feat recieves +2 negative damage instead, as he doesnt summon outsiders anymore.)
Binder of Fiends: At 3rd level, a demonologist gains the ability to call forth and bind a 9HD fiend (Erinyes for Lawful and Incubus for Neutral and Chaotic Demonologists) to aid him. This fiend remains under the demonologist’s control until unsummoned or slain; the fiend summoned becomes more powerful at 6th (12HD) and 9th (15HD) levels (gameplay note: this ability actually summons into the henchman slot, so a demonologist could conceivably have both their bound fiend and a summoned creature active simultaneously). A character who takes the full ten-level progression of Demonologist and who reaches a true level of 25 (this includes Level Adjustment) can summon an even more powerful 18-HD creature.
Fiendish Mantle: A demonologist who reaches 10th level gains resistance/10 to acid, cold, fire, and electricity.