Stags in Mythic+ Dungeons
Having at least one player in your party that can do offensive purges has become all but a requirement in higher Mythic+ dungeons (especially if you play Alliance and don't have access to the Blood Elf racial). Hunters are unique in that they can do both offensive magic purges and remove enrage effects (also known as tranq or soothe). The only downside is your pet must be in melee range of the target you want to purge, and the ability is on the pet's GCD so you sometimes need to wait a second before using it. There are several WeakAuras that will alert you when enemy targets have buffs you can purge such as this one
and this one
. Wowhead also has a guide
on all of the buffs your pet can remove in BfA dungeons if you'd rather research ahead of time.