What It Does
The line's signature — the tide, drawn and let go where the hand says, and the tide is the one who is still standing, and the one who cast it is the one who gave the blood, and the blood is the one the story remembers. It is the water school's answer to the fire door's cinder tongue: the tide does not burn, the tide takes.
The Cost
Circle 5 · Water · Exchange: blood — casting time three rounds. The Exchange is the blood rung on the ladder in The Veil: the spell costs exactly as much as the spell is, and the meter pays the budget, not the cost.
The Failure
The tide is let go shaped, and the shape is not the one the hand sent — the tide is the one who is still standing, and the one who is standing is the one the story is about.
In Stories
The archmage's water spell; the one the camp does not cast twice, because the camp is the one who remembers.
The door's scale anchor is Tidecaller, who casts it the way a hand casts a shadow — which is how a reader knows the shape of the thing, because the dragon does not think about it.