Let's start with the Goblin (again, I know). In D&D3.5 they are described as such:
"Goblins have flat faces, broad noses, pointed ears, wide mouths, and small sharp fangs. Their foreheads slope back, and their eyes are usually dull and glazed, varying in color from red to yellow. They walk upright, but their arms hang down almost to their knees. Goblins' skin color ranges from yellow through any shade of orange to a deep red; usually all members of a single tribe are about the same color. They wear clothing of dark leather, tending toward drab, soiled-looking colors"The Pendek a.k.a. The Short Men (using the same stats as the goblin)
"The Pendek, also called The Short Men by locals, are small creatures averaging around 3 feet tall, with rotund potbellies and disturbingly thin arms and legs. Its skin is s sickly shade of brownish-yellow with yellow, red, brown or black hair on its head arms and feet. The eyes of the Pendek are solid black, including what would normally be the "whites" of the eyes. While the Short Men are not particularly strong, they are quite clever and often set intricate traps or attack from unseen hiding places. Pendeks are omnivorous like humans, but once they smell or taste blood they go into a "Blood Frenzy" where they become ferocious (no statistical bonus, they merely do not back down and do not coordinate like usual). Pendeks have a coarse and simple language, that is akin to ancient humans languages. Their weapons and tools tend to be on the simple to moderately complex side with the most complexity appearing in their traps, including trip wires, counter balances and pressure switches."
In this way the "goblin" could be related to humans and even be an offshoot of an early pygmy-esque tribe.
Moving on to the Derro, this creature is not one that I personally have used often but is common enough that seasoned players could recognize it pretty quickly and (unconsciously) start metagaming.
"A small, stocky dwarflike creature in studded leather armor titters and mumbles to himself. His skin is a pale blue-white color, and his bulbous white eyes have no irises or pupils. His hair is coarse and white, and a long mustache droops past his chin. Derro appear to be some degenerate hybrid of dwarves and humans. Their rough skin is white with blue undertones and have sporadic tufts of coarse tan or pale blond hair. The eyes of the derro lack any visible pupils. Derro are degenerate and evil creatures of the underground, created from dwarf and human stock by some nameless deity of darkness and madness. Incredibly cruel and murderously insane, they enjoy taking slaves and torturing surface dwellers (especially humans) to death. Derro are afflicted by a form of racial madness, which most often manifests as delusions of grandeur coupled with an overpowering urge to inflict torment on other creatures" -From The Forgotten Realms Wikia Page
Replacing the description of the Derro with the following will entice your players to figure just what the hell this thing is.
The Minyak is a gangly creature standing at five feet tall. They are lanky and thin and covered in a greasy black substance that is secreted from its pores. The Essence of Minyak as it is called can be very slippery and very nauseating. The hair of the Minyak is jet black and covered in the Essence of Minyak miking it perpetually wet or greasy. Its skin is a dusky grey color, possibly even white, but stained by the black substance on its skin. The Minyaks hands are thin and long, tipped by sharp claws. When the Minyak attacks it strikes with a furious assault, swinging its claws wildly in an insane frenzy. If struck by the claws of the Minyak you could be infected by its poisons and suffer a terrifying madness that will make lash out at friend and foe alike."
Do you have any reskinned creatures? Please share them