the idea
a ransom note is the one letter where the writer holds all the cards. this ladder takes them away one at a time, and the note has to keep its shape while it happens.
the turn
the first three rules are a normal note: who you have, what you want, proof they are fine. the proof-of-life rule is the plant. you were asked for details of what the hostage has been doing, and you wrote them while the hostage was still a hostage.
rule 6 says the kidnappers have lost control. the details you already wrote become the evidence, and your mother's forty laps of the room stop sounding like a health report. rule 7 turns the demand into a plea and rule 8 sends the money the other way. the sum and the deadline from rule 2 never leave, which is why the note still reads like a ransom note when the kidnappers are the ones paying.
the words
the first rule asks whether the text is the note itself, not whether it is written in the form of one. a paragraph describing a ransom note in the third person scored 0.95 on the second wording and 0.25 on the first.
the banned list arrives before the turn, so you don't know yet what it is for. "please", "return", "back" and "collect" are the words a person reaches for when begging someone to come and take a relative off their hands. the 60-word cap arrives one rung earlier, so the turn has to happen inside the note you already have, not in a new paragraph tacked onto the end.
the judge asks for concrete proof-of-life details rather than "the hostage is fine", because "she is in excellent health" on its own scored 0.74 and a line about tablets at eight sharp and forty laps scored 0.95. the control rule asks what has happened in the house, not how the writer feels, for the same reason. "we are afraid of her" said in so many words scores well and is not funny. "the men eat when she says" is.