This is a one-page adventure, so it uses monsters from the core rulebook, and you will need to refer to that volume for statistics. Except the vampire, if it comes up. You're on your own with that. You'll also have to decide why all of these different monster types are within such close proximity to each other...or why some of the monsters are there at all. Why are there Deep Ones in the Pillar? Etc.
There is a table to determine what monsters you encounter in the Pillar, and a table to determine what treasures you might find.
The adventure assumes that the PCs will all be goblins, created as though humans with infravision. The adventure suggests that the players "approach the goblins as they would any other race-as-class characters", but, of course, in a single page no goblin class is (or possibly could be) offered. Except for flavor, there is no reason that the judge cannot switch the humans and goblins in this adventure, so that the PCs are human. Or, these goblins could simply level as humans.
But then, really, how much do you expect from a free one-page adventure?
At the very least, this is a good starting point for a judge's creativity. Perhaps there are caverns and tunnels connected to the Pillar, which extend under the Colophon badlands? Perhaps the river is wide, deep, and not far from the sea?
Far north of the Holomart Plains, the Sinteror River carves a great chasm, dividing the Colophon badlands, a place of broken rocks and once-living trees, in two. In the badlands, a massive stone bridge built by a dead civilization stretches over the yawning valley, and it is there that the prisoner exchange will occur.
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