I don't know if this is an official Halloween flavour, but it came out shortly after BOOtterscotch. Supposedly "Coffee Nut" is an award-winner, but I never heard about the contest.
I have to admit this one is a bit of a disappointment. The coffee flavour is so faint that you really only sense it as a bit of an aftertaste. They're pretty much a peanut M&M, which however is my favourite standard flavour, so it's not exactly a crushing disappointment. Still, I had been hoping for a bit more of a mocha hit. I still recommend them, just don't expect too much coffee.