It "hibernates" periodically during fights and becomes unattackable for the duration; summons when under 97% health; doesn't flurry; doesn't flee at low health.
Every time I have seen him he is between bb and fortress on that side of zone. Like the wisp and named gnoll not at all common. This round he only " Hibernated" once.
I got him there too after repeatedly killing the brown bear wandering on the hill between the fortress and Blackburrow (10 min respawn). He conned amiable to me (a druid). Even if it took me maybe 4-5 hits to kill him at level 95, he didn't hibernate once.