Fang-dagger

Bury it, water it with blood, and reap a monster.

An 8-inch fang lashed to a wooden hilt by fiber that never rots, strange carvings running the length of the blade. It likely came from a cynddaraig and carries blood-and-soil magic; in the hand it strikes for +1 damage. When you bury the dagger and water it with blood, a full-grown cynddaraig bursts from the soil — angry, confused, and hungry — and the dagger is gone, now just a tooth in its maw.