So, here's how I made the mask for my Rorschach costume. I'm sure I'll be tweaking it up to and possibly including Halloween, 'cos that's just how I am.
Through this process, I got to learn all about the "mending" setting on my ancient sewing machine, which is perfect for sewing knit fabrics.
I also got reasonably good at putting on and taking off all these layers quickly amidst all the fittings I've been doing.
This is the balaclava pattern that I used: [link]