A drider is a humanoid partially turned into a monstrous spider. The spider goddess Lolth subjects above-average 6th-level drow to a special test; those who fail become driders.
Driders are hated by drow, but often consider themselves specially blessed by their goddess and form their own expatriate cartels in which they work together sporadically under an air of intense distrust. They learn and expand their knowledge through loose information trades and temporary alliances. Thanks to these exchanges and individual experimentation, drider clerics, sorcerers, and wizards have learned how to effect the same change bestowed by their goddess on any humanoid. Though they consider their form to be a blessing, they know that changing other creatures into driders constitutes hideous torture. Drow-based driders enjoy the irony of their blessing being any other creature's bane.
Once changed, the creature is set loose to wander the Underdark alone. Other creatures, even other driders, seldom accept their company, though a drider may travel with spiders if he or she can stand to associate with the vermin. Regardless of origin, driders attack other creatures they find, normally through ambush. They greedily collect treasure from their kills.
Drow are generally amused by these rejects made in a reject's image, especially when a surface elf is made into a drider. However, drow do not suffer these aberrations to live any longer than they would a drider made from a drow. They do their laughing after the kill.
(Note: This information taken from wizards.com. Alternatively, you may play a Drider as the result of some sort of experiment. Furthermore, while it is stated in normal D&D that driders are always chaotic evil, your drider character need not be chaotic evil.)
Creating a Drider
The process of change is fairly involved. It takes three days to complete, working eight hours a day, but requires no special equipment or laboratory beyond the drider's innate sorcerous abilities. The creature changed must be helpless, but does not have to be conscious.
"Drider" is a template that can be added to any humanoid creature (referred to hereafter as the "base creature"). The creature's type changes to "aberration" and loses all subtypes. The new drider uses all the base creature's statistics and special abilities except as noted here.
Increase size one step over the base creature. The drider's new size determines its minimum Hit Dice, minimum natural armor, bite damage, and poison damage:
For purposes of Black Marches, do not add any racial hit die.
Changes to 30 ft., climb 15 ft.
Increase from the base creature as follows: Str +4, Dex +2, Con +8, Wis +2, Cha +2.
Natural armor rises to minimum natural armor. If the base creature already has greater than minimum natural armor, it keeps that natural armor.
The drider gains a bite attack if it does not already have one. It uses its own base attack. It can use its bite alone or as a natural secondary attack.
Bite damage depends on the drider's size. If the base creature already has a bite attack that deals more damage, it keeps that damage.
A drider retains all the special attacks of the base creature and also gains spell-like abilities and a poisonous bite.
1/day — dancing lights, darkness, detect chaos, detect evil, detect good, detect law, detect magic, faerie fire, and levitate. These abilities are as the spells cast by a sorcerer of the drider's sorcerer level (save DC 10 + Cha modifier + spell level). If the drider has no sorcerer levels, the abilities are cast as a 1st-level sorcerer.
Poison DC = 10 + 1/2 Hit Dice + Con modifier. The listed Strength damage from poison is both initial and secondary damage.
A drider retains the special qualities of the base creature and gains Spell Resistance equal to 11 + Hit Dice.
A drider receives a +4 racial bonus to Stealth checks.
Same as Base Creature +2