The Thunderclast

Weapon (maul), artifact (requires attunement by a by a goliath)

Otaras the Thunderdrake is a weapon of breathtaking and terrible beauty, a testament to both divine craftsmanship and the raw fury of mountain storms. Standing nearly seven feet in length, this colossal maul was forged from the eternal ice of the highest peaks and the living stone of Mt. Frioss itself. Eventually wielded by the goliath Ragnar Stormbane, it took on some of the essence of dragons from him.

It is a +2 Maul, which also grants resistance to lightning and thunder damage.

The Head: The weapon's massive striking head appears to be carved from a single block of storm-touched granite, its surface shot through with veins of silver-blue ice that never melts. Within the stone, crystalline formations catch and reflect light like captured lightning, creating an internal glow that pulses with each thunderclap in the distance. Runic inscriptions in the ancient Giant tongue spiral around the head, their letters filled with perpetually flowing ice-melt that somehow never drips away. 

The Haft: The handle stretches nearly five feet, hewn from iron-hard mountain oak that has been petrified by divine power and wrapped in strips of storm-giant leather. Where mortal hands might grip it, the wood has been carved with intricate geometric patterns that provide purchase even in the fiercest weather. Bands of the same silver-blue ice as found in the head encircle the haft at regular intervals, pulsing with inner cold-fire.

Divine Manifestations: When held by one deemed worthy, frost forms around the wielder's breath, and the faint sound of distant thunder emanates from the weapon itself. The ice veins within the head grow brighter with the wielder's determination, and in moments of great need, tiny lightning arcs dance between the stone and ice.

This weapon has the following mastery property. To use this property, you must have a feature that lets you use it.

Topple. If you hit a creature with this weapon, you can force the creature to make a Constitution saving throw (DC 8 plus the ability modifier used to make the attack roll and your Proficiency Bonus). On a failed save, the creature has the Prone condition.