(modified from rules as written)
Whelm is a powerful warhammer forged by dwarves and lost in the dungeon of White Plume Mountain. You gain a +3 bonus to attack and damage rolls made with this magic weapon.
Thrown Weapon. Whelm has the thrown property, with a normal range of 20 feet and a long range of 60 feet. When you hit with a ranged weapon attack using it, the target takes an extra 1d8 bludgeoning damage, or an extra 2d8 bludgeoning damage if the target is a giant or dragon. Each time you throw the weapon, it flies back to your hand after the attack. If you don't have a hand free, the weapon lands at your feet.
Shock Wave. You can use an action to strike the ground with Whelm and send a shock wave out from the point of impact. Each creature of your choice on the ground within 60 feet of that point must succeed on a DC 15 Constitution saving throw or become stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Once used, this property can't be used again until the next dawn.
Supernatural Awareness. You can use an action to cast detect evil and good or locate object from the weapon. Once you cast either spell, you can't cast it from the weapon again until the next dawn.
Sentience. Whelm is a sentient lawful neutral weapon with an Intelligence of 15, a Wisdom of 12, and a Charisma of 15. It has hearing and darkvision out to a range of 120 feet. The weapon communicates telepathically with its wielder and can speak, read, and understand Dwarvish. Giant, and Draconic. It shouts battle cries in Dwarvish when used in combat.
Personality. Whelm's purpose is to slaughter giants and dragons. It also seeks to protect dwarves against all enemies. Conflict arises if the wielder fails to destroy goblins and giants or to protect dwarves. Whelm has ties to the dwarf clan that created it, variously called the Dankil or the Hammerfist clan (it’s personality is because part of Whelm Hammerfist’s soul was embued into the weapon centuries ago). It longs to be returned to that clan. It would do anything to protect those dwarves from harm. A dwarven vampire named Ctenmiir may have been involved in stealing Whelm from the Hammerfist clan, and is now residing in White Plume Mountain as one of the wizard Keraptis’s guardians.
Thrown. If a weapon has the thrown property, you can throw the weapon to make a ranged attack. If the weapon is a melee weapon, you use the same ability modifier for that attack roll and damage roll that you would use for a melee attack with the weapon. For example, if you throw a handaxe, you use your Strength, but if you throw a dagger, you can use either your Strength or your Dexterity, since the dagger has the finesse property.
Versatile. This weapon can be used with one or two hands. A damage value in parentheses appears with the property — the damage when the weapon is used with two hands to make a melee attack.
Source: Dungeon Master’s Guide, page 218 with modifications from original rules