Just found this mask I knit a while ago, so naturally I had to put it on and run around the house making Zoidberg noises.
Free pattern: https://www.ravelry.com/patterns/library/dr-zoidberg
I was gonna find you one but having searched "knitting pattern Cthulhu mask" I found so many choices (including crochet patterns) that you'd better go look for yourself. And of course "knit Cthulhu mask" will include ones made by other people. October is coming, folks!