Ephemeral

Ephemeral was the Eternals' word for any mortal being from any planet in any galaxy. Being immortal and dwelling outside the realm of Time, the Eternals regard all Ephemerals as lesser beings and use them for their own purposes. (DW: Enlightenment)

Some Eternals would pose as gods and doom whole planets for their amusement. Under certain exceptional circumstances, sometimes against their will, an Eternal might enter the realm of the Ephemerals permanently, prey to age and death. (DWM: Uninvited Guest)

The Trickster described Sarah Jane Smith as "ephemeral." (SJA Whatever Happened to Sarah Jane?)