It is beatable, just a bit tight with the timing and its not explained that well, Im sorry. You probably just were too late and when picking up the mask and holding it. There's a sound que of a slithering sound when he's in the room, and you have enough time to turn around fumble with the masks, get the right one, and hold it on his face until he leaves. If the timing is right, you have the right mask, and you still die then it might bug that I don't know of. I'll try and do some further testing to see if I can find out of it is.
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It definitely wasn't due to being too late, I'd grab what looks like the opposite mask and wave it over its face ASAP and still die. :L But as said, I tried Every single mask, believe me, I replayed the game and had died probably around 15 times just to verify if I could find the right mask for the same face or not.