Stardust

Stardust never appears in a roll. The wiki classes it as developer-exclusive, so there is no odds figure, no biome and no event, and chumering is the credited creator. A note on its page adds that the aura is under investigation because it may have been removed back in Eon 1, and the wiki says it was discovered by one of its bureaucrats, IamIV, when asking developer 54_xyz for collection GIFs of unobtainable auras.

What you see is a large light blue star floating above the player inside a semi-transparent black cloud, with white particles falling from it. Two rings of swirling light blue and black aura surround the character, one at the torso and one near the ground, and a blue swirling portal sits under the feet, similar to Gravitational. The wiki says its basic design and theme are almost exactly those of Ethereal. The font is Merriweather. The aura has no ability and no in-game text. For a collector, it is a piece of the game's archaeology rather than a goal.