Green Watch was officially introduced as part of the Pony Vale questline and mobs were introduced in-game on February 4, 2014.
The Pony Vale questline involves a suspicious horse, Sadie, watching Green Watch. Sadie requests players to distract the druids while she searches through Green Watch supplies for evidences confirming that the druids are up to no good.
While distracting the druids, the player will meet Yarith Yewroot, one of the druid researchers at Green Watch. Yarith explains his observations of odd allergy-related behavior in Unicorn Forest, and assists the player in finding a cure.