If there are elves there are goblin elves. If there are apes there may be goblin apes. If there is a house which should not be able to stand, whose shadow kills the grass and whose silhouette on the hillside makes people avert their gaze, this is a goblin house. Put enough of those together and you’ve goblinly goblinned yourself quite a goblin city, one filled with goblins. Goblin your eyes.
Goblins are neither genus nor species. They are a kind, a type, and anything can become goblin, or come to be a goblin. Their language is incredibly goblin, and goblin goblins use the word “goblin” for many other parts of speech (numbers, definite articles, pronouns) we might recognize, with the rest of their language sounding like burbles, chittering, angry growls, and sorrowful moans.
Some folk don’t start out the way you see them now. Trolls are blessed/cursed with a kind of semi-stable cancer. True vampires have sold their souls to one of the stars above, and lesser vampires have been made franchisees to that relationship. The soldiers of the Pigment Mafia are called “made men” because they have been made into wererats.
Goblinism is contagious. Humans can catch it. Orcs can catch it. Foxlings, foxes, and fields of foxglove can catch it. Mostly you catch goblinism by eating goblin food, which is to say, food that’s caught goblinism.