@borderline i'm re-reading and I think the "Mercy" here refers to the thing the 3rd Floor Shadows said earlier: "
there's always a worthless pair in every debut. if Edward fails to find them, that's on him".
basically they MUST fail someone, or it's expected an examiner could weed out at least one of the candidates each debut. But Edward doesn't simply make it "impossible" for Emilyko to pass (with the implication that he totally would have, or other examiners would do such a thing). He still gave her a chance via the key being an option, he just committed the dick move of not telling her how important it is.
sure, it's messed up, but it would be more messed up if he did something that made it so that Emilyko 100% cannot pass the debut simply because he wants to be evaluated well as an "examiner" and having to fail someone no matter who it was. Example: setting up the rolling boulder thing on Emilyko instead of Ricky. that kinda thing would be the "no mercy" version of not letting Emilyko pass, I think.
TL;DR = "i gave you mercy" is probably just an inaccurate translation.