Step 1:
Fold in half over this line

Step 8:
Fold over these four lines.

Step 6:
Fold the flat part downwards.

Step 13:
Turn the model again.

Step 12:
Make an inside reverse fold on both edges.

Step 11:
Turn the model.

Step 10:
Press these four edges flat

Step 9:
Tape/glue these corners together, see upper line and the short line below

Step 5:
Press the part between these two arrows flat between your fingers, see next picture for help.

Step 7:
Press the model inwards a little. Do this by making a mountain-fold over the two inner lines and a valley-fold over the two outer lines.

Skeleton and zombie with an Origami cowboy hat

Step 3:
Press the layers between the arrows against each other, then prefold over the two lines.

Step 2:
Fold over these five lines, the line in the middle is the centerline.

Step 4:
Push the corner inwards by making an inside reverse fold over these three lines. The two diagonal lines are already prefolded.

Step 15:
Mountain-fold over these eight lines.

Step 14:
Mountain-fold over these four lines.

Done (cool) !                                                  Mr Skeleton is wearing a newer hat than Mr Zombie...

And this DIY-video by Joost Langeveld also has instructions for the comboy hat: