Mad Henryk

Likely a reference to Bloodborne on PS4.

The hunter Henryk goes mad and you must hunt him down with help from an NPC and kill him.

The item he drops, Worn Doll, is a reference to the doll that levels you up in the game.

[npc=109602] rare is located in Val'sharah 47.2 57.9

/way Val'sharah 47.2 57.9 Old Bear Trap

Mad Henryk spawns after you enter the trap on the ground.

Old Bear Trap kill and location video: https://www.youtube.com/watch?v=OAXthVw5Mow

Part of the Adventurer of Val'sharah
Drops [item=130214]
Here is doll demo: https://www.youtube.com/watch?v=kDsm1U6waRE

General info:
Rare level is scaled to your level, so it can be level 100-110. (Works everywhere except Suramar)
If your friend is 110 and you are 100 both of you can see different HP and different level, and still fight in the same phase.
Rare NPC in legion have almost instant respawn time (1-2 min max)
On first kill drops [currency=1220] and sometimes [item=138839]
[item=138839] can be buffed with [item=139390]

Note that this encounter seems to have a longer spawn time than the normal rares around the Broken Isles. Talking about 5 to 15 mins.