Set the lamp shade on its side on a piece of butcher paper. Carefully trace the shape of the lamp shade with a marker, rolling it along the paper until you've outlined the entire thing. Cut the shape from the butcher paper.
Secure the pattern to the shiny fabric of your choice, using sewing pins to attach.
Cut the shape from the fabric. Remove the sewing pins and the butcher paper pattern and set them aside.
Cut tentacles from the remaining fabric. The tentacles are strips of fabric that can be as long or short as you want. Cut them to be about 1/2 inch wide and sway the scissors as you cut to create wavy edges. You can choose to just make a few and scatter them around the lamp, make many of the same size, or switch it up and create tentacles of varying sizes.
Embellish the tentacles by attaching small rhinestones, beads, or sequins using a dot of fabric glue and a pair of tweezers. You can choose to add the embellishments randomly, or create a specific pattern for each tentacle. Wait for the tentacles to dry.
Apply a dollop of fabric glue to the top of each tentacle and press against the bottom inside edge of the lamp shade cover piece that you created with the butcher paper pattern. Wait for the lamp shade cover to dry.
Apply hot glue to the frame edges of the lamp shade. Wrap the jellyfish cover over the shade carefully, lining the fabric up so that the entire shade is covered. Allow the glue to dry before placing the shade on a lamp.