Create Soulstone

You consume a Soul Shard to create a Soulstone; a blacked gem that pulsates with life essence. While carrying this black gem and taking enough damage to fall unconscious but not die, the gem will crack open and revive the carrier. The holder returns to life with 1 Hit point. Having multiple Soulstones will not save the carrier multiple times, as carrying more will only cause them all to crack and be destroyed.

(See the Homebrewed spell Drain Soul for how to create a Soul Shard)