Goblinization is a plague upon the land, and one not often understood by adventurers until it is too late. All three predominant species of goblins (goblins proper, hobgoblins, and bugbears) have root cause in the same source:
Hags.
It is not unknown for those Devil-Witches Descendant to grow a third enchanted teat from which they naturally produce Witchmilk, a potent sorcerous elixir that transmogrifies those that drink it into bestial, horrific creatures of the Old Dark from which there is no change or escape. Their lives dramatically altered into the darkest mirror of themselves: Because all bugbears were once men and women of the world, hobgoblins youths and teens, and goblins children.
Children are preferred, and this is oft why witches are fond of kidnapping and secreting away with babes in the night. This also explains goblins’ magic so very well: it is a mockery of the non-sensical wild imaginations of those very beings they once were. This also explains their love for malicious pranks, especially on adults or those who have wronged children, and also why goblins will never hurt a child: they see themselves as children still. This is also why they remain servile to their witchmothers and kindly Grannies as Hags. Often, goblins will grow lonely, and seek to bring children back to their granmama for cookies and witchmilk, because they desire to quite literally make a friend. The goblin-transformation is so complete it perverts even the simple childish desire for companionship.
Hobgoblins are a different matter all together. Teenagers experience a constantly changing world of rebellion, half of the fruition into adulthood, and the angst of what often feels like being in the wrong parts of those two. But a Hag can offer an escape, an answer to their twisted and maligned bodies and broken feelings, an order to the madness of life. Youth in revolt now become orderly soldiers, stoic spartan warrior-kin, loyal to their god-queens beneath. No one ever listens, and now via the magical nature of their voice, whole tribes of smaller goblin-kind and rank and file hobgoblins and bugbears fall underneath their command and they execute other’s will, just as they are told.
Bugbears come from adults who fall prey to a Hag’s schemes, or worse: those who intentionally sought out a Hag for her power. Bugbears are brutish dunces gifted more of muscle than of mind, yet one has to wonder if this is a result of the transformation, or merely a common factor amongst those duped by those witchwork masters. No matter the case, their bodies now goblinized, bugbears are privvy to the ability to see in the dark and possessed of ogreish muscle and equally foul tempers. From their true goblin cousins they often learn to skulk and hide in the dark, and they are subject to hobgoblins’ commanding presence, often serving as shock-troops for whatever tactics they form. When all you have is a hammer...
This brings to mind the question of why Hags? And are all goblins servile to them? It certainly can seem that way, but isn’t necessarily the case. Sometimes Hags make goblins just because they can and move on, and other times they seek to craft a personal army. Often times goblins befriend or become attached to other creatures in lieu of their makers. Often times this creature is worse.