By the current picture, its mentioned he summons and enrages.
If the oracle gates to pop point and you are solo, depending on level and class, this winds up not being a pretty picture . . . for you, if the guards are up and you are at low health and mana and get summoned, LOL.
Gating causes him to regen to 33-34% health.
Doesn't always try to gate, and doesn't always successful casting when he tries, but just a heads up. Either clear the potential adds first, fight at his spawn point, or block his gate attempts if possible.