Pan-Dimensional Being

Pan-Dimensional Beings are an unnamed race of ancient aliens that were discovered and studied by Stanford Pines.

Overview
Most about Pan-Dimensional Beings such as what they physically look like are unknown, however during the episode, for just a brief moment, a Pan-Dimensional Being skeleton can be seen from within the background while both Dipper and Ford Pines search through their wrecked ship. Apparently they have at least four limbs possibly like tentacles which could imply that they could very well be cephalopods, they also wear strange helmets and according to the journal by Stanford Pines, Pan-Dimensional Beings can exist within seven to eleven different dimensions at once and they are even well known for a rather horrible sense of direction and through little is known about what Pan-dimensional Beings are like, expect that they come from some distant location known as Trilazzx Beta.

Over thirty millions years ago prior to the events of the show, 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 had formed the two bizarre floating cliffs surrounding above the entire landscape. Where the crew were either killed in the crash or died off in the passing of time.