Okay, forget my obscure, complicated plan. Most of your methods would work, I am just being picky.
On with the adventure!
Thinking quickly, you cram some food from your pack into the propulsion device and blast it past the shark. Just as it is about to eat the merman, the sudden movement catches its eye. The behemoth swivels its enormous head around to face the food, giving you a golden opportunity to grab your knife. Perhaps you can blind it in an eye or slash its nose so it cannot smell you out! While the shark hungrily devours the food, you creep up behind it, inching closer...closer...closer... Lifting your knife high, you slice downward forcefully. The shark's eyes dilate and it begins to thrash in agony, swirling the blood of its wounded nose with the water in garish stripes. You try to swim to escape, but the shark, enraged by your audacity to attack it, whips around and prepares to swallow you whole! Is this the end?
At the last second, the merman shoves you out of the way. You watch helplessly as monstrous jaws snap around the merman's scaly neck. You fear you are going to be next, but, surprisingly, the shark swims away with unimaginable speed until it is just a menacing speck in the distance.
Your tears mix with the saltwater as the merman's body floats gently to the sandy bottom. You knew your adventure would not always be happy, but it still pains you to think of how the merman sacrificed his life to save you. As you start getting ready to resurface and journey back home, you feel an icy band around your neck. It tightens, and a stiff voice says, "Save your false tears for the trial, Land-dweller. You will pay for murdering one of our brethren!" Your last memory is gasping for air before you black out.
You awake in a rigid chair with the taste of underwater-breathing seaweed in your mouth. Surrounding you is a roomy, cavernous stadium filled with merpeople. An official-looking one raps a rock on her desk and calls the assembly to order. You are reminded of the time you had to serve jury duty. The setup here is very similar, but with (you gulp) the merman's body in the center of the room as a piece of gory evidence. "The alleged murderer is awake," The official merwoman announces. "Let the trial begin."
Now, adventurers, it is up to you to defend your innocence. How can you convince the merpeople that you were not guilty of murder?
Please write an accusing and defending argument for the trial. The best one shall be used as your case. Remember, all evidence must be true!