Can only be used by hunters in the Beast Mastery spec. Minimum level 39 in Shadowlands.
You must learn the skill to tame Gargons, which is taught by a Gargon Training Manual, a guaranteed drop from Huntmaster Petrus, a rare NPC that can appear in the Witherfall Ruin area of south-east Revendreth.
Located in Sinfall, Revendreth. Lurking Monitors phase out completely once you adjust the Scorching Mirror during the quest Securing Sinfall. They initially look like statues. You have to aggro one to reveal which colour it is. Note that they don't appear on your beast tracker until aggroed.