The rarest Aura in Sol's RNG is Monarch at 1 in 3,000,000,000, though it's Challenged class and requires meeting a specific in-game condition first, the rarest standard-pool Aura without that requirement is Equinox at 1 in 2,500,000,000.

The Aegis Aura is rare at roughly 1 in 825,000,000, placing it in the Glorious tier, just below the top Transcendent-class Auras.

Starfall is a biome, not an Aura itself, while it's active, it boosts the odds of specific Auras like Starlight and Star Rider rolling.

You get the Oblivion Aura by crafting and using an Oblivion Potion, which gives roughly a 1 in 2,000 chance, making it far more accessible than most other named Auras.

Yes, you keep the Auras, Bundles, and Gamepasses included with my purchase, exactly as shown in the listing.