Believe it or not, this was the toughest part. I recently figured out how to make latex molds so I figured this would be easy. I carved four spikes from 1" wooden dowels and made a latex mold. I then got some 2-part 8lbs polyurethane flexible foam, mixed and poured. This approach worked fine when I was making skulls with ridged foam. The problem I discovered is that flexible foam is really hard to get out a a mold. It sticks more than the ridged foam and, since it flexes, there is nothing to push against. After ripping apart two of them, I just cut the others out, thus destroying the mold. I also found that this stuff is almost impossible to sand, so get the shape right or plan on using scissors.
So, I went to plan B and decided to do a two-part plaster mold of the spikes. Making this mold is not as easy as it looks but it isn't over the top difficult either.
Fortunately, I had one skull already completed and, just for fun, I painted a couple of the spikes and pushed them through the eye-sockets. Oooooh! Now I couldn't walk away. So, I went back to the latex, but this time, I used a thin line of clay jutting out from the wooden dowl so that I could make a seam. This seam would let me peal off the mold without cutting it. I used some binder clips to keep the mold closed during casting. Not perfect but acceptable by my standards.
I used scissors to trim the seam and to cut all the spikes to the same size (originally, I thought I wanted different lengths, but the mechanics of this approach didn't work out). Several rounds of this, a litter copper spray paint and a Velcro pad sown on the end, and I have my 26 spikes.
Now it is time to yell at you all. I have had several haunters ask for my help to duplicate this project for their haunt, which I am glad to do. However, there turns out to be a lot of you who want to skip this step and just use wooden spikes! "I will just be careful" you tell me. NO! DON'T BE CAREFUL, BE CERTAIN! If you can't make foam spikes, make hollow paper ones. Or cut up a foam pillow. Do something other than tangle real spikes over the kids' heads!