Seed of The Spinewondrous, very rare

This dark pebble is etched with minute circular patterns and has a single ridge running around its circumference. When you hold it you feel as if the earth itself is whispering to you, suggesting you swallow the pebble to get closer to it and understand it better. When swallowed, you notice nothing at all for 1d4 days, until you feel a sudden chill and stiffening along your spine. Over the next few minutes your skin darkens and hardens. Fractured plates of stone grow from underneath your skin on your arms, ribs, and jutting along your spine across your back. You gain resistance to piercing, slashing, and lightning damage as well as tremorsense out to 30 feet. Additionally, as an action, if you put your ear to the ground and concentrate as if concentrating on a spell you gain tremorsense out to 500 feet until you move from that spot or lose concentration, whichever comes first.

Curse. Once your flesh has started turning to stone you have vulnerability to Thunder damage. Additionally, while within sight of a chosen mountain each morning you hear it whisper to you, calling you to it, and you must succeed on a DC 8 Wisdom saving throw or spend that day compelled to walk towards the base of the peak. This compulsion is not mind control, and you do nothing rash to follow it, but it is a constant distraction and pull while you are not trying to travel towards the mountains. These effects, including your skin’s appearance, can not be reversed except by a Wish spell.

very rare