This boss shares his spawn points with four other bosses. He does not always appear.
This is a moderately difficult boss to kill, as he will use Restore Life on fallen mobs in the area which may include the dreaded Mahgo Hydras. Good tactics to use against him are Frozen Soil or interrupts.
An easy way to find him is to leave Ember Light Camp and then run towards the resurrection shrine, but do not pass beyond it. Looking at the rear of the shrine, turn to face the rock face. Move to your left as far as you can go. Press Ctrl and look for him at the spawn point west of you, if he is there carry on if not rezone until he is.
Be wary of the nearby patrols of Phantoms that move quickly and can overwhelm a party if multiple patrols are aggroed.
Assess what other creatures are with Rull Browbeater before rushing in. If it appears to be a mix of Mahgo Hydra and Igneous Ettins, this requires great care. Try to aggro a Hydra and spike it with damage. Once you have killed one, check to see if Browbeater is charging up Restore Life and interrupt it; otherwise, go back to dealing with the next hydra. You can now switch all your efforts to dealing with Rull Browbeater, effectively ignoring the other Ettin present, although killing the others may cause him to concentrate on resurrecting them, making him an easier target. Regardless, interrupt his Restore Life or concentrate on killing him.
If the battle is difficult and you need to rest or resurrect, move back towards the Seal and carefully resurrect the dead and heal before re-engaging. Running towards the seal usually breaks aggro with Browbeater along with any Hydra or Ettin that are with him.