The Needler Sentinel is a glitch that can be found on the level Quarantine Zone on any difficulty. It is a lone Sentinel which shoots Needler rounds, rather than the conventional Sentinel Beam and, when destroyed, drops a Needler. It can be found on the leftmost side of the first glowing orange indoor areas within the ruins of the Sentinel Constructor Factory. Note that this gun is perfectly ordinary, unlike the Scarab Gun. This Sentinel is an oversight from Bungie's tests with Sentinels using different weapons, and was meant to be deleted.[1]
It is equipped with energy shields, and has the same boost ability and flight capabilities that an ordinary Sentinel Major has. The only difference is the Needler rounds it fires. Bungie was originally planning to have certain Sentinels equipped with different weapons. When this idea was aborted, the Sentinel's model was meant to be deleted, but was most likely forgotten during the development of the game.