Thornwrack

Thornwrack causes long, painful thorns to grow out of the spell recipient's flesh, piercing the skin from the inside. One thorn appears each round, inflicting 1d3 points of damage, until all the thorns have appeared. When the number of thorns exceeds the subject's experience level or Hit Dice, a creature still conscious becomes immobilized by the pain, unable to take any action.

One round after the last thorn erupts from the subject's flesh, the first one disappears. The thorns continue receding at a rate of one per turn. Immobilized subjects can move again once the number of thorns falls below their Hit Dice or experience level. For instance, say the body of a 4th level wizard has seven thorns. After four turns had passed, only three thorns would remain, so the wizard would no longer be immobile.

Cure spells can restore hit points but do not eliminate the thorns. Dispel magic will end the spell but prevents existing thorns from receding. A heal spell cancels the thornwrack, eliminates all existing thorns, and cures all damage. Without the benefit of magical remedies, the spell ends when the last thorn has receded.