Blood Demon

Blood Demon was a Season Pass prize, so odds and luck have nothing to do with it. The Sol's RNG Wiki says it was the tier 50 reward of Season Pass V, added in the Boss Raid 2 update as an Event tier aura, and that season is over, so it is unobtainable now. Anyone who has it earned it by climbing the pass. khxlla, literally_starfall, TYINULTY and CoolJamesTheAwesome1 are credited.

The look is mostly red. The wiki compares it to Red Full Moon and Fragments of the Crimson Moon. The player hovers slightly above the ground holding a staff that closely resembles the one used by The Amalgamation boss, with a fast-spinning halo-like structure behind them and a red half-moon drifting past it. The aura gives the player two pairs of wing-like accessories, similar to the ones the Amalgamation uses in its second phase, while orange effects circle the player and red star-like particles stream up from the bottom.

Two notes stand out. It was the first Season Pass aura released without abilities, and its creator said some would come later, though that was described as unlikely soon.