Under some versions of D&D gnomes have the ability to communicate with "burrowing mammals". Do rats count? What about giant rats? Were-rats? Osquips? In a dungeon-centric campaign a gnomish adventurer with the ability to parlay with or interrogate giant rats could be about as useful as the elven ability to find secret doors. At least at low levels.
Now imagine an evil gnome living in your dungeon, constantly keeping the party under rodent surveillance.
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