Do not underestimate the power of the mask. You will see it on fans, decked out in their best Michael Myers cosplay for the Toronto Film Festival ‘s midnight premiere of Halloween — just two yahoos in dark blue coveralls rocking that bleached-out, rubber Shatner mug — and you will mildly shudder. You watch someone dressed as Myers walk onto the stage and stand there menacingly, a bit of post-intro performance art after director David Gordon Green and the cast have said their hellos, the lights dimmed to blackness, John Carpenter’s score barely being heard over the fanboy applause … and you will feel genuine chills. When this revisiting of the slasher-flick Rosetta stone’s mythology, one with more than a few callbacks and hat tips and some revisionist tweaks, makes a British true-crime podcaster — hello, 2018 — pull it out of a bag and hold it up, showing it to an institutionalized Myers, the dread in you will rise. And then, after Michael has escaped and killed some folks (this is sort of a spoiler, but really, is it though?) and actor Nick Castle, the original “Shape,” slips it on, the familiar blank face of one of the most…