Grovelthrash

Grovelthrash is a warhammer and one of the Arms of the Betrayers created by Torog from the soul of an ultroloth named Ciria. As a sentient weapon, it has a Neutral Evil alignment and can communicate with its wielder telepathically. Similar to a Vestige of Divergence, Grovelthrash progresses through various stages as it is wielded and gains new properties, including giving its wielder the ability to burrow through the earth, discern a lie more easily, deal retaliatory damage to their foes, and cast various spells.

Description
Grovelthrash is a warhammer made from a single piece of obsidian. Images of faces screaming in pain are carved into it. The warhammer was made from the soul of the ultroloth Ciria, who praises its wielder for claiming treasure and enjoys causing pain. Grovelthrash can hear up to a range of 120 feet and has darkvision for the same range.

Properties
Like all Arms of the Betrayers, it progresses through stages—dormant, awakened, and exalted—and becomes progressively more powerful as it is wielded. Each stage has all the properties of the previous stages.

Dormant State

 * One random minor beneficial property and one random minor detrimental property.
 * The wielder knows Abyssal and Infernal.
 * The wielder has a +1 bonus to attack and damage rolls made with this weapon.
 * Upon making a successful attack with this weapon, the wielder may choose to deal an extra 2d6 bludgeoning damage to the target. However the wielder also takes 1d6 psychic damage.
 * Advantage on Wisdom (Insight) checks to discern a lie spoken in any language the wielder understands while holding this weapon.

Awakened State

 * One additional random minor beneficial property and one additional random minor detrimental property.
 * The bonus to attack and damage rolls increases to +2.
 * The wielder gains a burrowing speed equal to their walking speed. They can burrow through sand, loose earth, mud or ice, but not solid rock.
 * When hit with an attack from a visible creature within 30 feet, the wielder can use a reaction to deal psychic damage to their attacker. The amount of damage is equal to the amount taken from the triggering attack. This feature can only be used while the wielder is wielding the warhammer, once per dawn.

Exalted State

 * One random major beneficial property.
 * The bonus to attack and damage rolls increases to +3.
 * When the wielder has fewer than half of their max hit points, the warhammer deals an additional 2d6 bludgeoning damage.
 * The wielder can burrow through solid rock at half speed, creating a 5-foot-diameter tunnel.
 * The wielder may cast the following spells once until the next dawn with a DC 17 save: Earthquake, Meld into Stone, and Stone Shape.