Ideas that feed into this:
- goblin-kind are invaders, usually brought here (or created) by Monster Summoning spells or cursed scrolls;
- their long-term goal is to bring more of their kind here and overrun the world;
- they are twisted creatures in behavior and form, with many breeds or sub-races;
- goblin spell-casters are rare, but goblins as a whole are inherently magical, as in fairy tales; they create magical items as a wizard, but their wares are as twisted as they are.
A "goblin level" for a megadungeon I might eventually do would include these regions:
- the goblin market, only active around the time of the new moon,
- the goblin warrens, with a couple prominent unique goblins and an entrance to a lower level,
- the heavily-trapped kobold tunnels, which are a major link between the outer world and underworld,
- the gnoblin lair, another link located in the deepest part of a forest,
- the forbidden tunnels known as The Death of Goblins, the lair of some nasty creature.