I've been running a 5e campaign in Yoon Suin and I've found that this edition of D&D works well with the setting... but a conversion for slugmen had to be made. Here is my humble attempt:
(quite note: my game has no multiclass and (almost) no feats)
ABILITY SCORES: +2 int, +1 wisdom. Slugmen have for generations favored mental acuity above all else, and most received a thorough education
AGE: Slugmen live to either 50 or 200-250 years, depending on if they can "Prove" themselves. (this will be explained in another post!)
Alignment: Slugmen tend to be lawful, being at the top of a intricate society. They tend to be somewhat indifferent to issues of good and evil.
Size: Slugmen are a bit shorter but stouter than humans (size medium)
Speed: Slugmen walking speed is 25 feet
Vision: Slugmen do not have darkvision but can see 360 degrees due to their flexible eye stalks. They can also look in different directions at the same time. However, their vision at very long rage is inferior to humans (normally won't affect in-game play).
Slippery: Slugmen's bodies are flexible and covered in a thin layer of mucus. They gain advantage in escaping magical or mundane bonds, grappling attempts, the tentacles of a monster etc. This does not protect vs paralysis however. They also have advantage to checks when trying to squeeze through a narrow opening.
Poison resistance: Slugmen consume so many teas, opiums etc that they have advantage on saves vs poisons, and resistance to poison damage. They can also eat almost anything.
Magic harmony: A slugman can attune to 4 magical items, not 3. The 4rth must be of lesser power (common, uncommon or rare)
Scholarly: The Slugman is proficient in one of the following skills: Arcana, History, Religion or Investigation
Language: You know both the trade tongue of the Yellow City as well as the Slugmen language