Lightning-spitting behirs are not quite dragons and not quite anything else. And that, in a nutshell, is what’s wonderful about them. Say you want an encounter that feels draconic, but for campaign reasons you’d like true dragons to be rare. Use a behir. PCs abusing dragon bane weapons? Surprise them with a behir—the villagers who come begging their aid certainly wouldn’t know the difference. Running a low-magic, primitive, or Viking campaign? Throw in a behir among the linnorms and drakes. Any time you need to emphasize otherness—throughout uncharted landscapes, foreign continents, and alien planets—behirs are a go-to monster.
The cyclopes of the Cassic Wastes ride behir steeds and war with the native perytons and slate-furred weretigers.
An advanced behir demands tribute from all who pass beneath his cliff face. But he is a devoted servant of an archaic deity of weather and endurance, and clerics and witches who revere similar powers might find him accommodating. He can also detect the presence of anyone who is oathsworn, naming them so aloud but offering no further comment or challenge (beyond his usual extortion).
Blue dragons and behirs typically loathe each other. But one ambitious blue dragon suzerain aspires to an empire, and consenting to clutch half-behir offspring would cement alliances across the desert.
—Pathfinder Bestiary 34