This was inspired by a recent article in Makezine's blog. Since that article was primarily photos, so I thought I'd note down the actual technique and some changes I made.

More information on this project is available at http://www.creatrope.com

Some of my Halloween work is also in other instructables:
PVC Mannequin
General Grievous with Mechanical Arms

Step 1: Forming the Skull

A godzilla/tyrannosaurus skull is formed from box cardboard. Two upper jaws, two lower jaws, and a 2" strip across the back and top, and a strip down the center top skull to the nose, and one running across the upper jaw and the snout. This is too coarse a lattice to lay paper-mache on (it will be too blocky), so a lattice of 1" masking tape forms a tighter grid.

The components are glued together with hot-glue (best) or white glue (and then staple the pieces so you can work immediately). I found staples were not enough to keep the skull stable.

Step 2: Covering & Painting

Covering

I used the paper mache recipe to cover
the outside with newsprint strips, let dry, repeat on the inside to cover the fragile lattice. It's best to cover anything you want to paint eventually.

At this point I did some dino plastic surgery, cutting down and shaping the jaw.

I added brow ridges to the original design by twisting some paper, taping place over the eye areas, then paper-mache'ing over those.

I let everything dry, then covered with a thin coat of mod podge to give it some further protection.

Painting

You'll need a thickish paint to cover the newsprint. I used an acrylic that I had laying around, combining several shades of green, barely, to put some textured streaks on the skull.

Step 3: Head Attachment & Eyes

Head Attachment

I built a custom 'helmet' to keep it seated firmly on my child's head.

Eyes

The eyes are formed from milky-white recycled halloween packaging plastic forms. Something shiny, reflective, thin enough to cut, translucent, and roundish. Since it was crushable, I put crumpled saran wrap inside to give it strength. I created two yellow LED eyes eyes using a 9v circuit. I got them coarsely into place working it under the foam and underneath the saran wrap in the eyes. The 9v battery simply tucks under the foam as well and is not glued so it can be turned on an off.

Step 4: Accessories

The jump-suit is a green overall.

A tail is formed from a large piece of triangular felt, with a base of about a 10" and a length of 2' or so, hot-gluing or sewing along one long edge, folding in half, letting dry. Turning it inside out so you have an attractive seam is optional. The tail was safety-pinned onto the jumpsuit for ease of removal.

The claw gloves are formed by roughly tracing the child's hand, pushing the fingers together, cutting two pieces, and then hot-gluing or sewing the two pieces. Note that it's easy to make them too small, so be generous in your sizing.

The plates are cut from cardboard, painted, then hot-glued onto a thin strip of cardboard. The cardboard strip has two safety pins hot-glued into it so the plates can be removed easily (you can't sit in a car with them). They are painted green base coat with white tips, like Godzilla.

See more pictures at www.creatrope.com