I like how they look and think a deepsea murloc makes a great hat.
I collect cashmere and other types of wool sweaters from thrift stores. I wash them in hot water to felt them, and use them to sew warm things for my family. Cashmere is softer and floppier than other types of wool. You could use another fuzzy fabric for this hat if you like. I've included a pdf pattern for this hat so you can make your own. I'll also explain my process for creating the pattern in step 1 in case you'd like to try your hand at making your own pattern.
I considered having the bioluminescent globe actually glow; I considered embedding a UV led in epoxy mixed with glow powder, coating it with more epoxy and glow powder until it was a decent sized teardrop shape. I could easily attach wires to that LED, run them through the forehead tendril, and attach them to two AA batteries.
I don't want batteries in my hat, though, especially since I plan on wearing it outside in the snow.
I used felted 100% cashmere for most of the hat, some polyfil batting for the insides of the appendages, craft foam for the spikes, and cotton flannel for the teeth.
Step 1: Designing Process
I first sketched how I wanted the hat to look. I had some cheap scraps of fleece and sewed them together to get the shape of hat I wanted. It took a few adjustments. I'd sew them, trim a bit if I didn't like the shape, then sewed the new seam. After I was happy with the general shape of the hat (without any added murloc parts), I cut the hat along the seams and traced the pieces onto paper, labeling each.
I cut some shapes out of more fleece for the legs, arms, eyes, etc. and arranged them on the pieced together hat to make sure they were the right proportion. After a couple fine adjustments, I traced those pieces as well.
Once I'd traced all the pieces I needed onto 8.5 x 11 inch paper, I scanned them and turned the images into a pdf. Now others can print out the pdf and trace the shapes onto their own fabric.