Clockwork

Clockwork hides a joke in its number: 530,000 is a nod to the username of the developer 53_Axis, and Prowler uses the same figure. It cannot be obtained in normal play. The Sol's RNG Wiki lists its rarity as Unobtainable, and it only appears in The Null's Existence, a biome that does not spawn naturally and has to be triggered by an admin or developer. Inside that biome the odds are 1 in 530,000, about 53,000 rolls at 10x luck, but that is a reference number rather than a goal you can chase. It is Event tier with no end date.

In game, the player floats slightly above the ground with an arm out, holding the hand of a clock whose tip shines. Small math problems appear above the head, linger and fade. Behind the title is a clockwork symbol, three white and neon gears hover around the player and white clock outlines spin under the feet in different directions. Its font is Fondamento, and the wiki says its subtitle is Clockwork, which stops the normal rarity line from showing. aakairoo, khxlla and Vk5278 are credited.