The god of stone, architecture, and strength does not waste time on whimsy or sentimentality. Still, giant constructions will not build themselves, and so Parshekkis the Huge sometimes gives his followers a gift to preserve them in these perilous times.
A Mountain’s Coin duplicates the blessing that the joga clerics of Parshekkis receive by virtue of their faith. The coin is sometimes found inside geodes mined in The Earthen Cradle, the sacred mine of Parshekkis, (excavated beneath the largest building in the world: a temple to Parshekkis). When found, the coin shows the giantish rune for “gift”. After the coin has been used, the rune changes to the one for “debt”. Unlike the clerics’ ability, this coin only works a single time.
It is often forgotten by the more distant cities, but Parshekkis is also the god of gold and banking. Debt is a common concept in his holy books. Furthermore, as the favorite brother of Mondaloa, the god of Death, Parshekkis the Huge is in a unique position to collect on what is owed him. A person that benefits from the usage of a Mountain’s Coin is expected to compensate Parshekkis for his “gift”. If this payment is not paid by donations (gold is preferred) or service, then the person’s transition into the afterlife will be delayed while their soul is forced to work off their debt. After Mondaloa judges a soul but before it is sent to its final destination, the Subterranean Angels of Parshekkis will appear and escort the soul to the site of their post-mortem labors.
After the the debt has been paid (in this life or the next), the face of the coin becomes blank. It is encouraged (although not required) that this piece of gold be invested wisely.
This ability only takes effect if the coin is being carried by a mortal, physical creature. Whenever the creature would be slain by physical damage, they are instantly turned to stone (at the exact moment they would normally die).
Whenever magical healing is used on the creature, the petrifaction effect instantly dispels itself (before the healing resolves).
An example might be useful. A player carrying one of these coins is killed by a giant’s spear thrust through the heart. The player drops to 0 HP (or whatever) and instantly turns to stone. The giant howls with dismay now that his spear is trapped in the stone PC, and breaks off the PC’s arm out of sheer grumpiness. Later, the PCs remove the wooden spear and cast a simple, low-level healing spell on the petrified PC. The PC returns to life badly injured and whines about how much blood is shooting out of his arm stump.
As for paying the debt, this might seem like a nasty trick to pull on a PC (especially if they consider items that they find to be free, or if they paid for the coin). Someone should probably tell them that they are in Parshekkis’ debt, eventually. Otherwise, it’ll be trickier to raise them from the dead if they are ghost slaves. Perhaps a sum of gold must be given to the church of Parshekkis before the soul is released, or the person can only be raised by clerics of Parshekkis (which will compound the interest, of course).
Use #1: Cheat Death. The coin really only helps with mundane, violent deaths. A person who turns to stone after falling from a great height might still be shattered into pieces (being turned to stone doesn't remove momentum). It might actually make it more difficult to retrieve a drowning victim. And if the PC is swallowed by a dragon, the corpse would probably stay in the dragon indefinitely (and make the dragon sad).
Use #2: Stasis Guardians. It’s not a medusa’s trophy room. It’s a bunch of defenders that will spring to life as soon as you trip the AoE healing trap in the middle of the room. (But hey, free healing).
Use #3: Lo, I Have Become Cargo. Sneak into a town as a decorative garden statue. Transport a dangerous wizard prisoner with ease. Bring the fire elemental prince through the Plane of Water without delivering a soggy ember.
You guys are creative. I’m sure you can think of more.
See also: River's Coin.