NOTE: I don't have a copy of the 5E Monster Manual yet. It's in the mail, should be here tomorrow. In the meantime, here's some things I thought up for flavoring various standard-issue monstrous humanoids to suit the dark fairy tale vibe of Vadhyislavia.
Hobgoblins are goblins that have acquired (begged, borrowed or stolen) a pair of iron-shod boots; after wearing these boots for a few hours, the goblin stands up straighter, it grows muscular, and it becomes crueler and more cunning. It is not unusual for a witch to keep a pair of iron-shod boots hanging from the rafters of her house or otherwise presenting a challenge to her goblin servants; the goblin with the initiative and inventiveness to claim the boots has earned the right to wear them and command the inferior goblins. A hobgoblin deprived of his boots shrinks down into a regular goblin after a few hours.
Hill Giants are a somewhat enigmatic race; largely resembling oversized ogres, their stooped posture, long arms, and short, bowed legs cause some scholars to speculate that Hill Giants are the hybrid offspring of ogres and the Gray Apes of the southern hills. Others claim that ogres are the "more civilized, refined" descendants of the savage Hill Giants. Regardless of their origin, it is well known that Hill Giants have an insatiable thirst for alcohol, and will quickly guzzle themselves into a stupor if liquor is presented to them. This weakness is the surest way to deal with a marauding Hill Giant; leave out a few casks of mead where it will find them, and when it's unconscious slit the brute's throat.