Tanks collecting Static Shock.
Every time boss moves over 4th purple circle he gain movement speed stack buff (+15%), so interrupt as much as possible or he will be too fast over time. Every 4th circle he will cast Static Discharge on everyone who have collected blue orbs! So if you have Static Shock debuff (random picked up, or you a tank) - go away from a raid. Good idea is to interrupt boss right before 4th circle.