From Compendium of Worldly Lore
This class is not for the faint of heart who hate spiders. This class weaponizes vermin and their abilities for your own usage, you get the ability to shape yourself into spiders, much like a Druid wild shapes into various other animals. You also gain the ability to envenomate your foes with a toxic touch and at the highest levels gain several abilities that spider has in addition to one of the most revolting abilities, to shoot a blast of normal sized spiders at people and make walls of sticky webs to keep people entrapped and deep within your web.
Role: Spell Utility
Characteristics: Arachnid focused casters, gaining poison touch and the ability to shape into spiders
Source: Underdark
Game Rule Information
The Arachnomancer has the following game statistics.
Abilities: Whatever your casting stat is, Charisma for dealing with vermin with your abilities, and dexterity for evading those who wish to stop your profane studies.
Alignment: Any Evil
Hit Die: d6
Starting Gold: N/A
Class Skills
The Arachnomancer's class skills are Climb (Str), Concentration (Con), Craft (any)(Int), Hide (Dex), Jump (Str), Knowledge (Underdark local)(Int), Knowledge (arcana)(Int), Knowledge (nature)(Int), Listen (Wis), Move Silently (Dex), Search (Int), Spellcraft (Int), and Spot (Wis).
Skill Points at 1st Level: (4 + Int modifier) × 4
Skill Points at Each Additional Level: 4 + Int modifier
Class Features
All of the following are class features of the Arachnomancer.
Weapon and Armor Proficiency: A Arachnomancer is proficient with whatever they were already proficient with prior to taking levels in this class.
Spells per Day/Spells Known: At 1st, 3rd, 4th, 6th, 7th, 9th, and 10th level, an arachnomancer gains new spells per day (and spells known, if applicable) as if he had also gained a level in a spellcasting class to which he belonged before adding the prestige class. He does not, however, gain any other benefit a character of that class would have gained (improved chance of turning or rebuking undead, metamagic or item creation feats, or the like). If the character had more than one spellcasting class before becoming an arachnomancer, the player must decide to which class to add each arachnomancer level for the purpose of determining spells per day, spells known, and overall caster level.
Poison Save Bonus: An arachnomancer adds his class level to all saves against poison.
Speak with Spiders Su: The arachnomancer can communicate with any spiderkind creature (see sidebar) as a free action. Mindless creatures can communicate and understand only extremely simple concepts (one word at best), but they generally don't try to eat someone who communicates with them.
Spider Magic: Add the following spells to the character's spell list (or to each spell list, if he has more than one):
0— Stick
1st— summon Small monstrous spider 1 ;
2nd— Spiderskin, summon Medium monstrous spider 1 ;
3rd— Neutralize Poison, Poison, summon Large monstrous spider 1 ;
4th— Giant Vermin (spiders only), Repel Vermin, summon Huge monstrous spider 1 ;
5th— spider plague 2 ;
6th— summon Gargantuan monstrous spider 1 ;
7th— Spider Shapes 3 ;
8th— summon Colossal monstrous spider 1 ;
9th— Shapechange (into spider or spiderkind creature only)
1 As Summon Monster, except that the spell summons one monstrous spider of the indicated size, 1d3 monstrous spiders one size category smaller, or 1d4+1 monstrous spiders two size categories smaller.
2 As Insect Plague, but summons spider swarms instead of locust swarms.
3 As Animal Shapes, but allows transformation into monstrous spider form only.
Spider magic spells are added to the character's class lists of available spells, so that he may choose them whenever he has the opportunity to acquire new spells of the appropriate level. He does not automatically learn them (in the case of a spellcaster who keeps spellbooks) or know them (in the case of a spellcaster who does not keep spellbooks).
Spiderform Su: Beginning at 2nd level, an arachnomancer may transform himself into a Small, Medium, or Large monstrous spider three times per day. At 5th level, he can also take the form of a Tiny or Huge monstrous spider, and at 8th level, he can take the form of a Gargantuan monstrous spider. This ability functions like polymorph, except that the indicated forms are the only ones available and the duration of the change is up to 10 minutes per arachnomancer level. Resuming normal form requires a standard action but does not provoke an attack of opportunity.
Venom Touch Ex: The arachnomancer can secrete poison as a free action. When he first gains this ability at 3rd level, his touch deals 1d4 points of Strength damage. The damage increases to 1d6 points at 6th level and to 1d8 points at 9th level. In each case, a successful Fortitude save (DC 10 + arachnomancer level + arachnomancer's Con modifier) halves the damage, to a minimum of 1 point. The arachnomancer's poison cannot be harvested or saved for any purpose.
Command Spiders Su: At 4th level, an arachnomancer gains the ability to compel any spider or spiderkind creature in the same way that an evil cleric can rebuke or command undead. The arachnomancer can attempt to command spiders a number of times per day equal to 3 + his Charisma modifier. He is treated as a cleric of a level equal to his character level (not arachnomancer level) for the purpose of turning checks and turning damage.
Webwalking Su: Beginning at 5th level, an arachnomancer can ignore webs (magical or nonmagical) as if affected by a freedom of movement spell. He can climb webs at his normal land speed without needing to make a Climb check and walk along webs without needing to make a Balance check.
Wall of Webs Sp: At 7th level, an arachnomancer gains the ability to create a wall-like barrier of webs once per day. Unlike the webs produced by the Web spell, those in the wall of webs are resistant to fire and as tough as steel. A wall of webs functions like the Wall of Iron spell (caster level equals arachnomancer level), except that an arachnomancer can use his webwalking ability to move through the wall unhindered, and any other creature can use Freedom of Movement to do the same.
Spider Blast Sp: Once per day, a 10th-level arachnomancer can produce a 50-footlong, cone-shaped blast of extremely poisonous, normal sized spiders. Every creature within the area of the blast takes 5d4 points of damage and must make 1d4 Fortitude saves against poison (DC 10 + arachnomancer level + arachnomancer's Con modifier; 1d6 points of Strength damage for both initial and secondary damage). Each creature is also allowed a Reflex save at the same DC for partial effect: Success means the victim takes half damage and need make only one Fortitude saving throw against poison (though the second saving throw normally required against a poison's secondary effect still applies). The spiders fade away at the end of the arachnomancer's turn.