Malgus is pretty straight forward, squishies should kite in the solo phase and always (ALWAYS) interrupt his force storm as it'll one shot the whole party. When he hits 10% and starts spamming force lightning, range him out on to the bridge (or just grapple him to the very edge) and have a person with a push attack chuck him over the edge. Note that if he is at the top of the stairs down to the edge of the bridge, he may get stuck and not go over the side. Lightning spam damage is not ridiculously bad and we've endured about 30 seconds of enraged FL due to a screwed up knock back before killing him.
Its not Force storm, its called Unlimited Power. You also get to see a buff when he is about to do it. He does it twice under 50%, one usually around 40ish and another around 10-20ish.