Prologues are wonderful in introducing the readers to your settings and building intrigue.
To make a good prologue, it must have a purpose in the overarching narrative. The author can also provide mysterious events and foreshadowing to catch the readers' attention better. It also gives readers what to expect later on the story. If the author's prologue shows melancholic and dark tones, it must maintain that tone to fulfill the readers' expectation.
Example:
Multitudinous voices exiled the silence within the tavern, each voices coalescing into incomprehensible murmurs to the average listener. A man sat by the counter, within his grasp is a glass of wine. His wide physique and scars spoke of his hardships, but his demeanor screamed joy as he indulged himself in alcohol. His voice loud, leaps towards the bartender, "Another one!" Plastered upon the bartender's face—a canvas of joy and money. The man before him was a regular, a loyal customer.
The bartender prepared the bottle and poured wine in his glass. The man drank excitedly with neither end nor cessation in between. Suddenly, he twitched, pain clenched his stomach. His experienced eyes gazed at the bartender who looked genuinely concern for him. If it's not him, then who, he thought. Slowly, his once lively demeanor died down, and he crashed against the floor. Dread ate away at his heart. Who... did... it, he thought. Soon, he blacked out.
