Diminutive, mysterious & inviolate race who control the Fallships which ply the vertical waterways linking the realms of the Underdark.
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The Boatmen take payment in peculiar coinage called Dash for their services, which comprise transport up & down the eternal waterfalls that link the different realms of the Underdark.
It is well-known in the Underdark that no-one crosses the Dark Boatmen nor causes trouble on their ships, not even the Aboleth, so travel on a Fallship is always perfectly safe.