When getting back from the crystal, once u reach the area where u have to put 3 orbs just ignore that and instead go in the open door which leads u to tanik's ketch. Once you're in the ketch a 10 minutes timer is gonna start and you're gonna kill the taken enemies asap. Note that when u kill the boss at the end you're not gonna be done and you'll have to kill all the adds to finish. Its pretty tough so make sure u have a good 3 man fireteam and try to burn through the enemies before reaching the boss as fast as possible