There is a Legacy version
here.

Skyfang Crystal
Item 12This Item may contain spoilers from the Season of Ghosts Adventure Path
Rare Invested Magical Source Season of Ghosts (Hardcover) pg. 304Price 2,000 gp
Usage worn;
Bulk —
A
skyfang crystal appears as a softly glowing length of blue crystal shaped like a gently curved fang; it’s typically affixed to a short length of chain, allowing it to be worn as a necklace or wrapped around a forearm. The light it sheds is equal in strength to that of a candle; it can’t be extinguished but can be blocked simply by wrapping the crystal in cloth, wearing it under clothing, or keeping it in a container. The first of these magical crystals was believed to have been created by a dying
dragon who’d spent her life fighting against evil spirits. She plucked a dozen of her smallest teeth from her jaw and offered them to her 12 most trusted allies so that they could continue to track down evil spirits and remain protected as they did so, even after she was gone. As long as you have a
skyfang crystal invested, you gain
mental resistance 10. If you’re
unholy, you’re
enfeebled 2 while you have a
skyfang crystal invested.
Activate—Seek the Unholy [two-actions] (
concentrate,
manipulate);
Frequency once per day;
Effect You touch the
skyfang crystal to your brow and utter the name of a specific
fiend or
spirit you seek. If the target is on the same plane as you, the skyfang crystal pulses stronger with light when you face in the approximate direction of the named creature, allowing you to
Track that creature. The DC for this check is equal to the creature’s Will DC, and you can use
Occultism,
Religion, or
Survival to attempt the check. As long as you’re tracking this fiend or spirit, you gain a +2 item bonus to saving throws against effects that creature generates. This effect persists until you activate the
skyfang crystal again to track a different target.