Very fun boss, but way to it annoying and you can just skip it.
Gravity Flux - you will be send away into the air with 1 hp left, aim into the green bubble/circle, or you will die. When you have landed in circle - wait till heals heal you and then go hit boss (he will be in MoO).
Gravity Swell - boss will pull everyone in big aoe to himself dealing massive damage, but all damage is shared - so more people puled, less damage everyone receiving.
Gravity Spike - circles around players, if you have circle just stand still and jump, and everyone else go out from you (same as Purges).