Prowler

Prowler is not obtainable by regular players. The Sol's RNG Wiki gives its rarity as N/A, and its home, The Hyperspace Realm, cannot spawn naturally: a developer who owns the aura has to start it. The page gives it an Event tier label and a 1 in 540,000 chance inside that biome, which would be about 540,000 rolls at 1x luck or 54,000 at 10x, but since no normal match ever reaches the biome, the number is reference data and not a plan. The entry also tags it as an effect-exclusive biome aura.

Visually it plays on the idea of traversing dimensions. A black star with a dark-blue outline and a faint blue glow roams behind the player, who floats above a half-formed dark-blue portal that leaks blue flames similar to Abyssal Hunter's. The player bobs up and down with both arms around another, whiter and brighter star. The music is Abandoned Post by Lemoncake, and 53_axis and rocca1080 are credited.