What It Does
The terms, set in the air between two fighters — the poison does not strike, and the poison does not chase, and the poison sets the terms, and the terms are the ones who are already losing. It is the master's poison spell: the argument is made before the fight, and the fight is the one who has to lose.
The Cost
Circle 4 · Poison · Exchange: reagent (bone, named) — casting time two rounds. On the ladder in The Veil, the reagent rung is the price.
The Failure
The bone is named wrong — the reagent is the forge's, not the one the spell wants — and the terms are set, and the terms are the ones who are already the one who is losing.
In Stories
The master's poison spell; the one the camp casts when the terms are the argument and the arithmetic is the one who has to win.
The door's scale anchor is Scorpion — the dragon casts it without thinking, which is how a reader learns the shape of the thing.