I made a giant caterpillar head out of chicken wire that had an articulating mouth just by leaving the gap open and letting the weight of the wire & paper move it. I had to do some trial and error adjusting for balance by cutting & tweaking the wire in between trying it on. Depending on the actual head shape, you can also start with something like a yoga ball you can deflate & remove once the papier mache is dry. Don't forget to put vaseline on the ball or it won't come out! Here's the caterpillar thing I made:
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This one is a lot bigger than it sounds like you're after. I mounted it on a back pack frame with wire so I could wear the whole thing:
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Cool! How heavy was it? I figured I might need back support as well. How long did it take you to make?

Holy canoli, chewy! That's incredible.

Sorry it took so long to get back to you sciurus. And thanks jrossi!

Lessee...it was probably less than 15 pounds. Just the head piece. It took me a total of about 30 hours maybe? The body was filled with 6 people who each held up a "rib".

I donated it to the natural history museum for their annual event called Bugfest, where you can eat chocolate covered grasshoppers and such!

We did make a much smaller head for a comic book dude the year before that was pretty light. As long as it has some way to secure it to your head but not come apart when you move, you're good to go. Maybe a bike helmet under the whole thing combined with a turtleneck would work. Email if you want more ideas or help!