Spiderform

Spiderform was a transmutation spell unique to clerics with the Drow domain. It turned the caster into either a drider or a spider.

Before 1372 DR
The caster could target several animals or one drow but the spell's effect differed depending on who or what it was cast on.

Cast on animals or arachnids, the targets turned into giant spiders with weaker poison, that caused those who succumbed to it to be stunned for a minute and slowed for the remaining duration but without any lethal danger. The giant spider thus made couldn't spin its own webs but could traverse other webs, including magical ones, without problems

Cast on a drow, the spell caused the targets to be turned into a drider. This drider was under the influence of the caster like a charmed creature was. This meant there were a number of limitations to the control the caster had over the target. It couldn't order it to do anything, that contradicted a superior's order, Lolth's orders, the target's own nature or its self-preservation.

1372 DR
By 1372 DR, the spell had new effects. It allowed the caster to turn into a Giant spider of varying size or a drider. Unlike the old version, the new version allowed the usage of the spider's full abilities including web spinning and poison.

Components
The spell's old version required verbal, somatic and material components in the form of a small spider that fit in the caster's hand, while the new version required instead a divine focus.

History
The spell was originally developed by the clergy of Lolth. Prior to 1372 DR, the spell was one of those spells whose usage didn't spill over into the other drow faiths, but by 1372DR, the spell went into usage of all drow churches.