I would like to have ship's kobolds, hobgoblins nesting in the ship by chance. Such a goblin causes unrest, you can hear his murmuring voice, it knocks, you hear footsteps of small and fast feet, it changes (a little) the sails, the course, the flag. If you are in deep thoughts - for example at the map table - the goblin quickly changes parts of your clothes, it steals your hat, changes your hairstyle, changes your equipment, repaints the ship, moves treasure around the ship. If a prank succeeds, it giggles. It gets drunk and then sings soft goblin shanties. It uses bananas, leaves banana peels on the floor on which you slip and leaves stains on the nautical chart. Because it's shy, you only see it's footprints on the floor, fading away as you look on them.
A goblin can only enter the ship at outposts. If you have a goblin on board, you have to look past the critical points (steering wheel, anchor, supplies, ...) more often. The goblin is shy, it doesn't show up then. If it can't show itself, because the pirates are vigilantly on patrol, it becomes grumpy and scolds quietly. You don't understand his language, but you notice how it gets angry.
There is only one way to get rid of the leprechaun: it has panic-stricken fear of chickens. When a ship arrives on board, you hear the goblin scream in fright and then whimper quietly. A chicken in the crow's nest drives the goblin away, it will immediately leave the ship at the next outpost.
