From Destinypedia, the Destiny wiki
Barrier Knights are powerful Champions of the Hive, armed with the ability to envelop himself in an immune shield when threatened. Behaves like an ordinary Knight until it losses a decent amount of health, where they then envelop themselves in a dome-shield while they regenerate, they are still capable of firing in this stance. To prevent this, the/a Guardian should use Anti-Barrier mods from the Seasonal Artifact, where the specialized bullets should be fired directly at the Knight to stagger and expose him to all damage.
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