Vow Of The Spider Queen( Drow of the Underdark, p. 55)
You have taken an unspeakable vow to further the interests of the Spider Queen at all costs.
This unspeakable vow grants a variety of supernatural benefits, but at a terrible price.You gain immunity to poison. When using the Verminfriend feat, you gain a +5 insight bonus on the Charisma check, and you can prevent any single vermin within 30 feet from attacking you. If you succeed, the affected vermin cannot attack you for 24 hours. Also, you can expend a rebuke undead attempt to rebuke or command vermin. This ability functions like rebuke undead, except that it affects vermin. Finally, you develop horrid glands in your mouth that allow you to spit a wad of toxic fluid. Your glands produce enough poison to spit a number of times per day equal to 3 + your Con bonus (if any). Treat this as a ranged touch attack with a range increment of 10 feet. A direct hit deals 1d6 points of acid damage and forces the target to succeed on a Fortitude save (DC 10 + 1/2 your level + your Con modifier) or take 1d4 points of Strength damage. Ten rounds later, the target must succeed on a second save against the same DC or take an additional 1d4 points of Strength damage. Every creature within 5 feet of the target takes 1 point of acid damage from the splash.
To fulfill your vow, you must not cause harm to any vermin. You may not deal lethal damage or ability damage to such creatures through spells or weapons, though you can deal nonlethal damage. You may not target them with death effects, disintegrate, or other spells that have the immediate potential to cause death or great harm. You also may not use nondamaging spells to incapacitate or weaken vermin so your allies can kill them.In addition, once per week, you must perform a horrid ritual that involves opening yourself to the maddening presence of the Spider Queen. The ritual takes 8 hours, and at the end of this time you take 1d8 points of Wisdom damage. Wisdom damage can be healed normally. If you intentionally break this vow or fail to perform the profane ritual, Lolth finds you wanting. If you have 11 or fewer HD, you immediately transform into a chwidencha (see page 108), becoming a scuttling thing with no memory of your former self. If you have 12 or more HD, you immediately become a drider. In both cases, you automatically lose the benefit of this feat and may not select a new one to replace it. If you break your vow because of magical compulsion, or otherwise unintentionally, you lose the benefit of this feat until you perform a suitable penance and receive an atonement spell.