A bubbling black Celestial potion that grants a random level 10-15 combat skill stolen from a high-level Sheol demon.
The sole contents of Carl's Celestial Heavy Metal Box in chapter 10, this potion sat in a bottle shaped like a horned skull with a handwritten note reading "Drink Me" beside a doodle of a demon hand throwing devil horns. The liquid inside was black and bubbling, each bursting bubble releasing a spurt of color that reminded Carl of the space chicken story. The system described it as part of the Borant Corporation-era escalation, wanting the crawlers as deadly as possible: drinking it grants a random level 10 to 15 Celestial-tier combat skill the drinker doesn't already have, and because it is hell-kissed, that skill is drawn from any Sheol-level mob of level 200 or higher.
Mordecai was literally shaking when he saw it, calling it a Celestial-quality skill potion and rushing it to the Crafting Room to examine. He returned to announce he could learn to craft them, given a few more table upgrades and very specialized ingredients. The bottle itself spoke in a deep demonic voice, urging Carl to drink it deep and put it inside him. Carl drank it manually; it tasted like ass, the bottle let out an almost sexual groan as it dissipated into dust, and Carl briefly saw and felt the burning hellscape of Sheol before receiving Gloom Wraith Phase.
A small glittering bottle shaped like a horned skull, filled with bubbling black liquid, a handwritten 'Drink Me' note tied around the neck.
The Celestial-tier reward that gave Carl his most dangerous new combat skill.