Nightmare and Pirates

Error, a coal-black merman with amethyst-shimmering fins, was splashing in the waves when an ominous shadow fell over his carefree existence. A net, woven from coarse fibers, tightened around him. Panic seared through his mind. He had fallen into the hands of pirates.

On the deck of the pirate ship, under the gaze of Captain Nightmare, Error writhed in futile attempts to break free. Nightmare, his face scarred and eyes full of grim determination, watched him. His loyal cutthroats crowded around: Dust, with a manic glint in his eyes; Killer, whose smirk was as sharp as his blade; Horror, who emanated a foul stench of decay; and Cross, silent and morose.

Any attempt to touch him was met with fierce resistance. Error's tail, powerful and flexible, crashed down on the unwelcome guests with the force of a storm. Dust tried to grab his fin but was sent flying, clutching broken fingers. Killer, chuckling, tried to flank him from behind, only to receive a painful blow to the jaw.

Nightmare, maintaining an icy composure, raised his hand. The pirates stepped back. He approached Error, his shadow looming over him. "Well now, sea devil," he hissed, "let's see what kind of treasure you are." Threat echoed in his voice, but deep within his dark eyes, an unreadable interest flickered. The game had only just begun.

The pirates caught a male mermaid.
The pirates have everything they need to catch mermaids: a special muzzle to prevent the mermaid from hypnotizing anyone with her music, thick ropes, and blindfolds just in case, because there are rumors that mermaids can freeze a person with a glance.
A mermaid's kiss signified gratitude, meaning that whoever a mermaid kissed would never drown. However, forcibly kissing a mermaid would result in death. A mermaid's tears could heal any illness or wound, but could not bring the dead back to life. A mermaid could transform into a human when on land. A mermaid's bite caused poisoning and seasickness.