I flash spam until he start acid rain. Then wait for the cast bar to finish and run the slugs to ralf. I TP The boss to keep my MP up and continue to spam flash.
(We don't kill any slugs)

If you are doing the super slug do the same as above but after the slug pops voke, HG and halone combo it. Leave the other 2 slugs alive and hold them while TPing the boss.