A Hand of the Wychlaran Side Trek
From the introduction:
In ages past, devils and demons roamed the countryside of Rashemen, and groups of Raumathari fiend hunters, called Olkin, hunted the creatures. The Olkin knew the immortal nature of their prey, and as a result, each hunting party included a member versed in arcane magic and a member knowledgeable in the worship of nature. When the hunters successfully captured a fiend, they would strap it to large boulder similar to Devil’s Rest. The Olkin’s casters would then perform a complex ritual that wove together both natural and arcane magic, binding the immortal soul of their prey in the stone.
An encounter for 3rd level characters