Corrupt Thiroc the Redeemer 0/1 (Sul Vius: Demiplane of Life)
Attack Thiroc the Redeemer, when it de aggros, Zone back to Sul Vius: Demiplane of Decay and right click the Decay Spike
*** Might be worth mentioning that when the spike is clicked in decay, someone has to be in life watching the mob die. If you don't do that, the task does not update and you have to wait for the mob to respawn to try again. (Task window is very specific about that part)