Lizardfolk are most often used solely as a plot hook for low-level adventurers.
The situation is almost always that a humanoid village is located near a lizardfolk swamp.
The two races have generally had good relations in the past (with the unspoken understanding that they stay out of each other's territory), but in recent months, the lizardfolk have taken to raiding farms, harassing travelers and generally making life miserable for the villagers, all with no explanation.
The PCs are sent to deal with the problem, and they'll either kill all the lizardfolk or more often, find something the villagers have accidentally done that is making life difficult for the lizardfolk.
Yes, I think that pretty much sums up every lizardfolk encounter I've ever seen.
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