Obsidian

Obsidian is a naturally occurring volcanic glass.

Sources

Obsidian is formed when lava cools rapidly in sea water. This process was not widely understood on Foon until a geologist from Earth explained it in an email to Hello From the Magic Tavern.¹ Large deposits of obsidian are found in the mines of Bornea.

+ Warning! Spoilers Inside for Season Three. Click to reveal

A potential source of more obsidian was the Black Spire Volcano, located on an island. To prevent the creation of new obsidian, the Dark Lord had his forces permanently divert the lava.²

Magical Properties

Usidore's Arm

+ Warning! Spoilers Inside for Season Two. Click to reveal

During his time administering Dark Lord-controlled Hogsface, Usidore's hand and eventually his whole arm turn to obsidian,³ which he attributes to the evil of working with the Dark Lord. Jyn’Leeviyah the Red also experiences a corruption of a limb, her leg, when she makes a truce with the Dark Lord, but rubbing it against Usidore's arm cures her.⁴

Usidore eventually learns his arm has the ability to destroy the Void,⁵ and begins to plot a way to deliver his arm to its center. Before solving how to do so, his arm is swapped with Sarah Maher's when the two switch places during Usidore's trans-dimensional travel,⁶ and is shot into space with Sarah due to a spell by Can the Yellow.⁷

The arm (along with Sarah) finds its way to Space Bunker High Command & is indeed instrumental in the destruction of the Void.⁸

Obsidian Doom/Usidore's Hand

Obsidian Doom is an obsidian sword with powerful magical properties, including the ability to permanently kill a wizard. It was forged by the Necromancer Dripfang LeDesparé

+ Warning! Spoilers Inside for Season Three. Click to reveal

Dripfang created the weapon using a variety of magical artifacts stolen from The Jizzlenob Preparatory School For Young Wizards. His plan was to win the the Dark Lord's favor by killing the wizard Usidore, but the blade instead ended up embedded in Arnie Niekamp nearly killing him.⁹

Its magical nature makes it unsafe to remove the blade even after Arnie's condition is stabilized, so blade stays embedded in Arnie's chest for almost a year until it is separated from him during a time travel experience. The blade now free and available to use against the Dark Lord, Chunt suggests they rename the blade Usidore's Hand, in reference to the period in which Usidore's hand had turned to stone.¹⁰

Besides the power to permanently kill a wizard, the sword can also cut through the crystalline barriers that appeared throughout Foon as a result of The Shattering.

The Shattering

+ Warning! Spoilers Inside for Season Three. Click to reveal

During the magical phenomenon the Shattering, Arnor the Warrior also discovered obsidian could break the crystalline walls that had sprung up throughout Foon. He emptied the mines of Bornea gathering enough obsidian to break the walls throughout Foon.

Footnotes

1. Season 3, Ep 80 - "Usidore's Hat"

2. Season 3, Ep 101 = "Volcano"

3. Season 2, Ep 45 – "Night of the Oversharing Dead"

4. Season 2, Ep 57 – "Jyn’Leeviyah Returns"

5. Season 2, Ep 63 – "Genie"

6. Season 2, Ep 87 – "Blue and Green"

7. Season 2, Ep 86 — "Season 2, Ep 86 – Hogsface and Chicago"

8. INTERLUDE – "Hello from the Future"

9. Season 3, Ep 21 – "The Lurking Phantom"

10. Season 3, Ep 70 - "Arnor's Next Feat"