Found some rubbery spike things. Probably from some Bionicle set. Spraypainted them black, and added a post to each which plugs into the holes in Poseidon’s hands. I’d prefer biggger ones, but they scratch that itch.
They are Bionicle interestingly enough they are called Kratta. They go inside the Rhaskshi. Apologies it’s been years since I saw the names but I know how to pronounce them if I don’t know how to spell them, but that is a fairly neat idea