You must kill the rounds of plasma snake and cruor guys in the pool area to make him change positions and become agro.
Mob can be burned in under a minute with the right raid setup. Mob has very low HP. CA will teleport his current target every 30-45 secs right to his sitting position in the water after he is aggro. Fighting him in the water at his position is most recommended place to deal with the teleport.
His Disease AE is very potent and ticks very fast, have cure disease potions ready on everyone in your groups to save your healers from stopping to heal.