The Tortoise Curse

In the wastes of Lower Druk Yul, where only the occasional grasshopperman tribe wanders by but otherwise the wind is left to its own devices, there are kurgans - burial mounds - made from the dessicated husks of huge, long dead tortoises. Only the shells remain, hollowed out, along with the contents which ancient people put there.

There are a dozen of these kurgans dotted across an area of 100 or so square miles. They are so far from civilization that they are largely unknown and untouched. Each contains TT: B, along with something or somebody dead. Breaking into any of the tombs brings a curse on the head of the first interloper to enter. Slowly but surely he or she is transformed into a tortoise; the process takes 6 weeks and cannot be lifted except by a remove curse spell. This halts the effects but does not reverse them - the curse can only be completely cured by a wish spell. Mechanical effects are as follows and are cumulative until the transformation is complete:

First week: skin toughens and back hardens (+1 bonus to AC)
Second week: back curves and hunches (+1 bonus to AC, -2 DEX, -2 CHA)
Third week: mouth forms into beak (gets an extra bite attack doing d3 damage)
Fourth week: back hunches further and hardens into a carapace (+1 AC, -2 to hit)
Fifth week: limbs stiffen and standing becomes difficult (+3 damage from strength, -2 to hit)
Sixth week: character becomes a tortoise, without the ability to function in human society - though he or she retains sentience.