It's in wowhead:
New general skill:
Wailing Arrow : Fire and enchanted arrow, dealing (185% of Attack power) Shadow damage to your target and an additional (75% of Attack power) Shadow damage to all enemies within 8 yds of your target. Targets struck by Wailing Arrow are silenced for 5 sec.
100 yard ranged (100 yard?? o__O)
This skill belongs to Sylvanas in the HOTS game.
I had already heard that it would be a unlocked skill if you caught the legendary bow in the new Raid. But it looks like they decided to make it a "general skill".
https://ptr.wowhead.com/news/patch-9...stincts-322661