A traveler is a creature visiting the Emerald Dream either by dreams or by direct planar travel (if they are powerful enough). Furbolgs, naga, ogres, pandaren, quilboar, trolls, and other humanoids are commonly encountered travelers.
A significant number of creatures can be found the plane that are merely dream visitors. Some of these creatures are present only for a single dream, while others appear frequently. Many cats, for example, cross into the Emerald Dream on a regular basis. While their bodies sleep, their twitching paws and quivering whiskers signify they are quite active once they cross between planes.
Cats and other mammals are not the only living things to make the crossing. Any intelligent creature can dream and therefore enter the plane of dreams, even without realizing what it has done. Creatures of nature do this most frequently, but even monsters sometimes make the crossing; dragons, gryphons, and even ancients are known to visit the Emerald Dream and might be encountered by other visitors.