From Destinypedia, the Destiny wiki
When summoned, the Blocker immediately closes down the bank it was sent to, preventing the enemy from banking their motes. While in combat Blockers fight the same way as most variations of that Taken enemy.
In Gambit Prime the blockers had been switched. Now 5-9 was a Elite Taken Goblin, 10-14 was a Taken Centurion, and 15 was an Ultra Taken Knight. If the disabled bank was left unattended and more than one blocker was active, the bank would begin to be drained, siphoning motes from that teams bank into the enemy's until the blockers were dealt with.
With Beyond Light's release and the sunsetting of Gambit Prime and the Reckoning, vanilla Gambit was merged with Prime to make the currently final iteration of Gambit and the Blocker system. The Blocker roles were carried over from Gambit Prime.
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