From Destinypedia, the Destiny wiki
Spotter Shanks fight like normal Tracer Shanks, hovering in place and firing their Wire Rifle at the player. Their main function is to provide an immunity shield to Iriks. The fight will start with Iriks already having three Spotter Shanks protecting him. When they are destroyed, he will be vulnerable and summon Fallen reinforcements. Every third of his health, Iriks will call three more Spotter Shanks, who will shield him again until destroyed.
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