Titan-EX is a fight where you need to memorize the patterns and be able to react accordingly. My suggestion if u are having trouble is to actually stand furthest back from the party if you suffer from lag so u have a larger margin of error available to you and if you are hit by a plume its only your plume and you wont die. 90% of plume deaths are a result of people not stacking properly. Another trick is instead of running abck or to the side run to the tank, Titan only AOE's before a Mountain Buster and that only happens after he does a landslide.