A goblin market is an instant trove of plot hooks that could start a campaign or reboot a campaign that's struggling to find reasons for the PCs to care.
Here's how it works...
The PCs encounter a strange creature or market of strange creatures who offer to sell them fantastic, impossible things. The sellers might be the devil, spirits, faeries, goblins, aliens, Mi-Go, demons, mysterious angels, djinn, an AI system, or gods. If you're running a Planescape D&D game, you should probably introduce this trope at least once. It could be a single mysterious tempter or a community or structure full of eerie deal-makers, or even an actual market (like in Changeling).
Nothing for sale is entirely straightforward, but all of them seem useful and maybe even life-changing. Some may seem like curses, except when you think about them, they would be very useful. They sell magic items, magic powers, magic properties, and fates. Here's a sample menu of things on offer:
- The ability to fly when the sun is shining
- Immortality, but not agelessness
- The ability to psychicly hear anyone's negative thoughts about you
- A sword that, no matter what happens, is guaranteed to kill the person whose name you etch indelibly into its blade
- Invincibility, until you kill a person
- The guarantee that you will become wealthy within a year and a day
- The guarantee that you will always lose when you play a game of chance (try betting that the serial killer won't leave a clue that leads to their arrest, for instance)
- The dangerous blessing that all locks open with ease in your presence
- A wand that can teleport you anywhere in the world that you name
The price for these blessings is never money. The creatures that you trade with wind up asking bizarre, intangible prices. The bargain you make with them is magical and binding. These costs come in two categories: Geasa and pieces of your identity. Geasa are compulsions or magically-enforced agreements. Usually the blessing-seller names their price. But sometimes the shoppers can make counter-offers or even offer some part of themselves or some promise as payment. Here are some example costs:
- Your memories of your childhood
- The promise to return to this same exact place in a year and a day
- A promise to never eat meat again
- Your name
- A small favor to be named in the next year and a day (they really like "year and a day" time-frames)
- Your face (don't worry - you'll get a loaner for the term of the bargain)
- The next lucky thing that will happen to you (happens to the goblin instead)
- Your first born child
- Your voice (Disney used this trope for the plot of The Little Mermaid)
Some of these prices are heavier than others. That's OK. None of them can really be measured against one another anyway.
The GM trick with Goblin Bargains is this:
- Whatever the blessing, the GM has to turn it into a curse at least once. Every single example I listed can be turned to cause a player to sweat. The invincible character may feel like she doesn't need to kill anyone, since she can withstand any harm. But when a truly monstrous villain threatens the life of an innocent, and it becomes a life or death struggle, what does she do? Does she preserve her power?
- The price has to be way worse than it seems at first. For instance, if a player trades for "striking beauty" and gives away their face (which seems like a low price since they're getting a strikingly beautiful one in return), they may find themselves the subject of a statewide manhunt for the crime of serial abductions -- committed by the faerie using their face! For the duration of the deal (year and a day of course), they can lay low with their new face. But when their time is up...
The plot that a goblin market can create is immense. Here are some examples:
- Getting out of a bad bargain or finding a loophole
- Buying back your lost identity
- Making a better bargain, or even trying to come out ahead in a deal with the devil
- Using your new blessing to achieve the thing you wanted it for
- Covering up your deal with the devil from those who would rightly judge you for it
- Getting trapped by unintended deals, just for speaking the wrong words; then trying to get out of them
The reason the "goblin market" works to excite players about your game is that they can make a deal to get things they care about, to achieve goals they care about. In return, they pay a cost that motivates them to avoid the drawbacks of their bargain, or even to try to get out of it. That's fuel for many, many sessions of play.