In heroic mode, Keristrasza does the same as normal mode, so you have to keep moving at all times to avoid getting too many stacks of the debuff she puts on you, but she also freezes you to the spot, so you can not move.
I tried standing in one spot and jumping a lot. This did not only remove the debuff, but I also avoided several of those freezing buffs by jumping.
So jump jump jump, pretend it's PvP.
by rompefjert