A folktale

Truth Seeds

There's this old tale, about an old herb tender from Marshedge that tricks a fen-troll into eating an enchanted seedpod. She promises to go get the troll more food if he promises to then let her go. Of course, the troll breaks his word and tries to eat her, but the seedpod bursts into a mass of gwir-nettles when he does.

To unlock it, you need one of the following:

• a Marshedge herbalist, steeped in lore, to teach you the ritual;
• the spirit of a gwir-nettle, friendly or bound, to reveal the secrets of its birth.

Truth Seeds

When you soak a pair of gwir-nettle seedpods in your own blood, whisper secrets over them, and say the words of power, they become truth seeds (magical).

When you and another each eat a truth seed and make promises to each other, the seeds stay in your guts and ensure that the promises are kept.

When you break your promise, the truth seed in your gut sprouts violently into a full-grown gwir-nettle, dealing 1d10+3 damage with advantage (messy, ignores armor) — and now you've got a gwir-nettle growing out of you.

If the other party breaks their promise, they suffer the same fate.