Here are the basics to making any mascot head. Each head costs about $4 in Fabric and then whatever extras you want to add.

Step 1: Paper Mache

I buy the large punch balloons and paper mache the whole thing with about 4 layers. Let dry overnight. Pop the balloon and cut the hole in the bottom for your head.

Step 2: Making the Head Durable

Cut the mouth however you want it. This will be what you see through. You can also cut the eyes too if you want more vision. I use cardboard strips around the bottom and around the mouth/ eyes to make it stronger.

Step 3: Fabric

Measure around the head and the height. cut fabric needed and then cut it into 4 pieces.. Top to bottom. cut each strip to a point at one end. sew all your sides to each other all the way through your points and slip over the head. cut a slit for the mouth or eyes and fold back and glue on the inside. At this time if you want to add some stuffing to bulk up cheeks or brows you can and then glue the bottom to the inside as well.
Now you're ready to start creating your character.

Step 4: Adding the Extras

I use see through fabric for the mouth and or eyes. glued to the inside. You can add wigs, hats or anything else. I sometimes use Styrofoam balls for noses ( painted with acrylic paints).

Monster from the muppets I didn't use almuch fabric. i bought regular yarn and hot glued it.

I use foam for the eyes or teeth. Any additional piece like ears or snouts i sew like making a pocket, stuffed and hand sew on.

The clown I used an actual clown wig and cut it into pieces. His teeth are foam with some red paint on them.

The red clown with the blue nose.... I covered in brown fabric and then with the red. There are large eyes cut, no mouth but the red fabric is see through.

The monkey has eyes and a mouth cut and covered in sheer fabric. The snout is structured with cardboard, stuffed and then hand sewn on.