Piercing Howl is a warrior ability available at level 19 for those with the Fury specialization. It is an AoE Shout debuff that costs 10 Rage. It snares nearby enemies (50% Movement Speed) for 15 seconds and is unaffected by diminishing returns.
It provides a rudimentary method of dealing with runners, as unlike Hamstring, it does not require a successful melee hit and, unlike Hamstring, can be used in defensive stance which is particularly helpful for tanks. It also offers a useful method of escaping from a fight gone bad, slowing all pursuers enough for the Warrior to get a decent head start.
Note that the only effect this has is on enemy movement. It does not do damage, or debuff enemy combat ability at all, so is of no real use during a hectic melee furball. Instead, use Thunder Clap, which affects attack speeds as well.
Piercing Howl is safe to use around any crowd controled opponents, precisely because it does no damage, although it is a hostile act, so will aggro any neutral mobs in range.
Available for use in all stances and does not have any weapon requirements.