Yes, I'm talking about that shield on the ground, however in HM you need a synergy to activate it. The problem here is that you can pretty much never get it to work for all four players, that's why I think it may be bugged. We only ever got it once to work for all four group members. I have seen that you can still beat the HM by using a different tactic (using the AOEs from the adds), but I doubt that's intended.
On hm there are four ways to avoid the one shot. Standing in the poison fountain, standing in the ice freeze, getting hit by the stone laser beam and taking the shield. Each player needs to take one.
The killing of the adds needs to be timed so some of those options are up every 20%. Everyone of those ccs will only protect you from the one shot and not other damage so it's best imo if the healer takes the shield as its the only option that won't stun you.
The stone laser beam requires that person to be broken out of it with a synergy so it's best a dps takes that and not the tank so the boss can be taunted asap after the one shot phase is over.
The whole fight is chaotic and fun. The hm is a night and day difference then normal. Good luck!