Prawn cocktails with the prawns made to look like maggots.
Or something like a large ground pink crab cake with prawns coming off like fingers off a palm, you could put something spooky on the palm. You could always use a dollop of marie rose sauce to make the palm as well.
A thick red soup to resemble blood or greeen to resemble goo.
You could do baked fish, slit the fish to open in a coffin like shape and put something like veg to rememble something in the coffin, could also use a baked aubergine for this.
I do wonder about my imagination sometimes!!!