Stolas's Grimoire

"You will be entrusted with the study of the Earth's skies, the stars, the prophecies they hold, all that stuff. Isn’t that fun? You will begin the studies of your grimoire, which will grant you access to the mortal realm to study and observe, and you will grow to be a mighty Prince of Hell, with your own legions to lead and pass on your knowledge to!"

- Paimon, to a young Stolas

Stolas's Grimoire is an arcane book belonging to Stolas that is used by the I.M.P company to illegally access the living world. It was gifted to the former by his father on his birthday in "The Circus".

Description
In the Helluva Boss pilot, it had a burgundy cover with dull yellow markings and the crown symbol that is on the walls of Stolas's mansion on the front with white pages.

The Grimoire was redesigned for the main series and now has a navy blue cover with gold reflective pages separated by a dark burgundy ribbon, and has golden borders with a large red gem on the center of its spine.

The front cover is emblazoned with a moon encircling the real-life Goetic seal of Stolas, along with four stars which resemble upside down crosses.

When used, the portal glows red on the rim. However, in the episode "Loo Loo Land", it is shown for a second that the portal can be different colors such as blue, though the book was held via Stolas's telekinesis at the time, suggesting it was activated by his magic.

Background
The exact nature of the Grimoire isn't clear, but, Stolas was entrusted with it to carry out unknown duties in Hell, and one of its abilities is to allow the opening of portals between Hell and the living world.

Eventually, it came into the possession of Blitzo, I.M.P's founder, who stole the book off Stolas after sleeping with him. It became an essential part of the company's business model of travelling to the living world to assassinate targets on behalf of souls damned to Hell. Stolas does not seem to mind lending it to Blitzo, albeit with the vague remark of "less than legally", hoping to bribe him with its use for continuing their monthly affair.

In the episode "Harvest Moon Festival" one of Stolas's duties with the book is shown as he travels to the Wrath Ring for the festival of the same name. There, as part of the ceremony celebrating the harvest, he uses the book to open a portal showing an actual Harvest Moon. Though, this seems to be mostly for ceremonial purposes.

Trivia

 * According to the storyboards of "Murder Family", Blitzo supposedly refers to the grimoire as a "Hocus pocus book". However, the line was cut in the actual episode.
 * It is implied in the actual episode that Stolas only requires the grimoire once a month for some form of unnamed ritual.
 * In "Loo Loo Land" Stolas is shown using the book to travel to a star system that is in the process of being destroyed, indicating the grimoire's portal creating abilities are not limited to just planetary bodies like Earth. Additionally, the grimoire is shown to share the same astrological aesthetic as Stolas, hinting it may also have abilities related to the stars.
 * In "Harvest Moon Festival" Stolas mentions cursing the harvest with the glow of a true harvest moon, though this may simply be more of a ceremonial blessing.
 * The official real-life version of the grimoire is approximately 8.5 inches tall.
 * The text on the page Loona has opened in "Truth Seekers" when translated using the runic alphabet says "How to open this stupid fucking portal" and "These bad drawings", respectively.
 * In "Seeing Stars", it is implied by Stolas that anyone can use the grimoire's spells without the help of the book itself, if the user can memorize said spells.
 * In "Western Energy", it is revealed through Stolas and Blitzo's text conversations that the former does not necessarily need the book every month.