Being a ruler of a vast kingdom entails the responsibility for a hell of lot of subjects. In Neptune's case these subjects are scaly, slimy, slippery, tentacly and don't smell good if left a few days out in the warmth. For them it is the utmost a living being can achieve (being scaly, slimy…etc.). So if an innocent vessel with innocent people comes along and asks for admission to the kingdom, the greets honor is to be baptized with just these things.
And here's what you need: Take a broth with indistinct pieces of fish and, well, stuff, prepare a thick paste of cream that got sour mixed with battered eggwhite and shaving foam, have plenty of eggs at the ready (the old ones work best), as well as sufficient ice water. What else do you need? Oh yes, rope to tie the delinquents to their chairs, a huge syringe to inject the foul brew into the mouth. And the cakes! Make them as dry as possible so nobody can swallow them. Ever. Instead add spices, and more spices. And then some.
Well, here's a few images. Have fun!