Paul started out making his costumes from paper mache. It’s an accessible, cheap medium that can be used to create just about any shape, large or small. The results can be sturdy and weatherproof if done right. It can also be heavy and uncomfortable. But it’s a time honored Halloween costume material and I’ve gathered some links that show it’s versatility and potential high quality (no balloon heads). I also threw in some cardboard, duct tape and plaster gauze links.

Let’s start with this Joker mask at Ultimate Paper Mache because it shows the basic technique that you did in elementary school but with some refinements that make it much cooler.  Jonni Good has developed a homemade paper clay recipe that she used on the Joker mask. There’s a video showing how she makes it .

She says after 50 years of doing paper mache the old fashioned way, she now uses this exclusively
“because it allows me to create fine details easily, it dries extremely hard
when applied in a very thin layer (1/8 to 1/4″ thick) and the clay dries
much faster than traditional paper mache pulp.”

She also has a tutorial on making a urethane mold that the paper clay can be used in.

Some helmets:
Spartan helmet
Helmets from duct tape + cardboard + fiberglass resin (scroll down a bit) their examples are pretty cool

inanimate object costumes:
cardboard jenga costume
Mr. Peanut from instructables

Plaster Gauze:
Video on making a plaster gauze mardi gras style mask
Look at these fine examples of plaster gauze masks.  These are sculpted over plasticine forms.

See the amazing full size robot (Transformer) costume! Tutorial using cardboard by Intrxtc.

Every costumer needs a dress form and they are EXPENSIVE. Try making your own:
plaster/paper mache dress form
duct tape dress form (there’s also a paper tape version)

Radical puppetry giant heads:
Make giant masks for the street.  I had another life once making big puppet heads as comunity art projects back in Los Angeles. I made the lens to share the technique.
This big head is 360 degrees and so could be adapted for a mascot type costume or a portrait of a particular person (I was imagining Elvis actually, with a sparkley suit).
Some street puppet inspirations – Bread and Puppet, Heart of the Beast, Paperhand

Professional paper mache-ers for inspiration:
Sergio Bustamente
Masks by artist and performer Michael Cooper
The Art of the Mask Etsy shop