Hello fellow raiders, I've done this part on all classes so I've killed a few of these gatekeepers. My advise is to only use the R2(trigger on PS systems) heavy attack. The reason for this is the knockback that is caused by the attack. Just open up with the heavy and keep pushing it and the gatekeeper is as crippled and helpless against you as he is when you use a Striker Titan Suppressor granade. Hence I've done it on Titan too and I dont use my granade as it is useless when he does not stand a chance against the heavy attack. So at lvl 31 he dies from 3 hits and on lvl 30 its 4 or 5 heavy attacks. Enjoy am out ---> P.S. Back to work, took ages to write this post with customers bumping in. Might take awhile for me to answer if there is further q's.