First, cover your work surface and the flood in front of it with heavy paper. The plaster can get EVERYWHERE.
Fill your small bucket with warm water, and cut your plaster tape into manageable lengths - a foot or two, depending on how comfortable you are with it.
Generously coat your gazing ball with vaseline, set aside (but close at hand!).
Starting at what will be the bottom end of the staff, use the plaster tape to sculpt directly onto the dowel. One piece at a time, dip a strip of plaster into water, bunch it up lengthwise (to make a long, narrow piece), and apply it to the dowel. I wind pieces up almost the entire length of it, smoothing as I go - you want to get rid of the "mesh" look.
Once I've got the initial bunched pieces applied, I'll go over it with un-bunched pieces, smoothing and sculpting as I go. The goal is to make it look like a gnarled tree branch.
Working quickly and carefully, make three bunched up pieces into long "fingers, attach at roughly equal distances around the top end of the staff. Secure with more un-bunched plaster, around the dowel.
Position the greased up gazing ball at the top of the dowel, form the 4 "fingers" up and around the ball. Add a few smaller "fingers" to connect and create more of a branched-off design.
Allow staff to dry completely, usually overnight.
Paint the staff all over with 2 coats of a dark brown acrylic paint. Be very careful when painting up around the gazing ball, and be sure all plaster is hidden by paint. Allow to dry completely.
Using a toothpick or pointed sculpting tool, carefully scrape away any plaster spaltter on the gazing ball, and clean up the edges of the "branches" that encase it. Touch up any newly exposed plaster with more of the dark brown acrylic paint.
Once dark brown paint has dried, use a smallish paint brush and black paint to paint "shadows" in all of the ruts, etc. Take a look at movie screen caps for an idea of how much black there should be (it was a VERY dark staff!). Allow to dry fully.
Use a grey acrylic paint SPARINGLY to paint some highlights on the high points of the staff. Allow to fully dry.
Once you're happy with the paint job on your staff, use a soft brush to coat the entire staff (plaster only, not the gazing ball) with polyurethane varnish. Allow to dry completely, paint a second coat on, and once again allow to dry completely.
Use small pieces of paper towel or toilet paper to GENTLY AND CAREFULLY polish off any remaining vaseline on the gazing ball... and, you're done!