Mariner

Sadly as you suspected, it does not work.

The response creates a lasting effect, hovering over the Mariner, waiting to kill it. There is little said about lasting effects, but there is no reason to believe that being insane shakes them off (I think only leaving play would usually be enough).

The response does require the card still be named Mariner at the end of phase in order to carry out its grisly purpose, but insane characters keep their names, so no luck there either.

I understand your reasoning, RichardPlunkett.  Allow me to just play devil's advocate for a moment.

Awhile back, I talked about Azathoth on the Bone Sculptor page.  I expressed my opinion that blanking Azathoth (say, by using Called by Azathoth), would prevent the "end of game" effect to occur.  I reasoned that passive effects are similar to Forced Responses except they're harder to counter since they're not triggered effects.  However, the game still waits for the specified moment to check and resolve the passive effect, same as with a Forced Response.

Now, perhaps my opinion on that was incorrect, but I feel like the same logic should, in theory, apply here.  I believe the rules say an insane character retains only its name, its descriptor, and its uniqueness.  So, isn't insanity effectively like blanking?  If Azathoth can be "turned off" by CbA, shouldn't Mariner be turned off by insanity for the same reason?

I'm asking because I honestly don't know.  I was skeptical when I first raised the question because my instincts on CoC usually seem to be at odds with the reality.

I'm with Richard on this. It's a lasting effect, so the text only has to be present when the Response is triggered, not when it finally takes its toll on the Mariner.

Agreed.  Passive effects are different.  Azathoth doesn't trigger until later, so you can blank him beforehand to stop it from happening.  Mariner triggers up front, so it's too late to blank him - the effect is already out there.

I see.  Makes sense.  Thanks, all.