Smashing Leap - Breaks land platform and causes it to submerge into lava
AOE knockback to all players
Adds spawn throughout encounter
Frenzy - Boss breaks apart the current island he is on
Normal Strategy
The boss should be tanked on one side of the island; Ranged will be on the opposite side; Melee should stack behind the boss for AOE heals and to avoid the cleave.
Off-tank will pick up adds when they spawn, these should be AOE'd down immediately.
Throughout the fight, the boss will knock back all players into the lava. Just run back to the platform ASAP; the lava adds a DoT.
The boss will also break apart the land platform you're fighting on. You will be able to know when this is happening because a warning prompts you, saying "Gharj is about to Frenzy." At this point, a path will open to another platform; Run to the next platform immediately; Take any adds with you, then DPS them down.
Hard Mode Strategy
There is no difference in hard mode, other than more damage. Use the same strategy as normal mode.
When transitioning to another island, be sure to keep your Grav Round stacks up.
If Gharj is between you and the path to the new island, run around Gharj, through the lava, rather than under Gharj. This will save you from a potential 1-shot.
5-second Recap
Boss cleaves, keep at range if not melee.
DPS adds immediately when they spawn.
When knocked into lava, get back to the platform immediately.
Quickly move to next platform when yours breaks down.