Pan-Dimensional Being

Pan-Dimensional Beings are an unnamed race of ancient aliens from the animated series, Gravity Falls.

Biology
Although the Pan-Dimensional Beings never made an exact physical appearance however, in the episode Dipper and Mabel vs The Future, skeletal remains of one is shown briefly in the background of the ship as Dipper and Ford Pines were exploring their wreaked spacecraft. Judging by from its' looks, Pan-Dimensional Beings have at least several limbs resembling sets of tentacles (this could very well imply that that are like some sort of cephalopods), wear strange helmets and according to Stanford Pine's journal, they are able to exist in seven to eleven different dimensions and are rather bad in what is referred to as "horrible sense of direction".

History
Little is known about wha Pan-dimensional Beings are like, expect that they come from some distant location known as Trilazzx Beta. While 30 millions years prior to the animated series' events, a spacecraft piloted by a group of Pan-Dimensional Beings somehow crash-landed on Earth which created the valley that would one day be Gravity Falls, Oregon as the impact formed the two bizarre floating cliffs surrounding the entire land.

Well it is unclear if whether the crew aboard the wreck ship were killed in the crash or died off in the passing of time while their spacecraft was soon buried beneath the surface.