Unless your story is set in the Barbados, there are exactly two uses for tridents in fiction. The first is for anyone associated with the sea, particularly if you're a fisherman or a god. This isn't contrived; tridents have their origins as fishing tools, after all, and Poseidon was portrayed with a great big trident. The second is if you're evil. Really evil. Tridents don't go to moderately evil villains or Redshirts; if you're using a trident you better be Satan or seriously, ridiculously evil, and a major villain. They're too stylish for Mooks. Examples of Prongs of Poseidon include: