Weapon (warhammer), artifact (requires attunement)
300 years ago, Thor, the Norse god of thunder, battled the gargantuan clay golem, Mökkurkálfi. Their conflict could be felt from hundreds of miles away, as Thor summoned a ferocious storm to do battle with the construct.
When their battle led them near to the east coast of Duran, Mökkurkálfi struck Thor down from the sky, causing him to lose his grip on his mighty hammer, Mjölnir. The hammer would land with a meteoric impact just east of the Frost Fells, which quickly attracted the attention of the Order of Arkiah.
The order was quick to arrive at the landing site. Deciding the hammer was worthy of study, they transported it back to Abeldour, the order’s headquarters, which took the combined efforts of the entire Inner Circle.
The hammer was meticulously studied by the School of Artifice within the order for several years, though little progress was made. The largest breakthrough was the deciphering of the runes engraved on the hammer’s surface. They read, “I am Mjölnir, I am the bane of giants, I am the herald of thunder, fear ye mighty, and despair”.
One man, however, discovered the secrets of the hammer. A human named Varys Uthadar, a promising young wizard of the School of Artifice, found a way to wield Mjölnir. Drunk with his newfound power, Uthadar killed hundreds of innocents in the name of discovering the hammer’s full potential.
Eventually, despite Mjölnir’s power, the Sentinels of Arkiah were able to hunt down and defeat Uthadar. The archmage of the time decided that the hammer was no longer secure in Abeldour. As such, they passed the hammer into the care of Miiraevos, the golden dragon beneath the fortress city of Rovannen. It now resides within his horde, awaiting someone with the strength to wield it.
Magic Weapon. Mjölnir is a magic weapon that grants a +3 bonus to attack and damage rolls made with it. The hammer does an additional 1d8 thunder damage on hit. Due to its unaturally short handle, the hammer does not have the versatile property.
Thunder's Onus. In order to lift the hammer and attune to it, your Strength score must be 25 or higher, and you must be attuned to either the gauntlets of ogre power, or the gauntlets of wielding.
Thrown Weapon. Mjölnir has the thrown property with a normal range of 40 feet and a long range of 120 feet. Immedietly after the attack, the hammer flies back to your hand. If you do not have a hand free, it lands at your feet.
Giant's Bane. Attacks made with Mjölnir against giants do an additional 2d8 thunder damage. When you roll a 20 on an attack roll made with this hammer against a giant, the giant must succeed on a Constitution saving throw (DC 17) or die.
Pendant. While you are attuned to Mjölnir, you can will the hammer to shrink down to the size of a pendant, which can be worn on a neckchain. While in pendant form, the strength requirement to lift the hammer does not apply. You can shrink or expand Mjölnir as a single object interaction on your turn.
Magic. Mjölnir has 10 charges. While holding it, you can use an action to expend 1 or more of its charges to cast one of the following spells from it, (DC 17): ceremony (1 charge), destructive wave (4 charges), thunderous smite (1 charge), thunderwave (5th-level version, 3 charges).
Other Properties. Mjölnir is believed to possess powers far beyond what Varys Uthadar displayed during his rampage. The School of Artifice within the Order of Arkiah believe that, when wielded by an entity of sufficient strength, Mjölnir could retain cataclysmic destructive potential.
Destroying the Hammer. In order to destroy Mjölnir, it must be cleaved in two and metled down by the god of the fire giants, Surtr. Only when the metal of the hammer has been melted completely to slag, is the hammer permanently destroyed.