Whelm is one of three infamous magical weapons introduced to Dungeons & Dragons in the 1st edition Advanced Dungeons & Dragons module "S2: White Plume Mountain". Alongside its siblings Blackrazor and Wave, this weapon has managed to make an appearance in every single edition of the game, from 1st through to 5th, an honor that can't be shared with their oft-forgotten sibling, Frostrazor.
Perhaps the most humble of the three White Plume Weapons, Whelm is an enchanted throwing hammer of dwarven make, infamously guarded by the vampire Ctenmiir. Simple and straight-forward, Whelm tends to exemplify "dwarfish values", as best as those are defined in their edition.
In 1st edition, Whelm is an intelligent +3 hammer (+5 hammer for dwarves) with Int 15 and Ego 18 whose driving purpose is to slay all of the monstrous enemies of dwarfdom - trolls, giants and goblinoids. Whelm can detect the presence of gold, gems and goblins, and has the powers of a Hammer of Stunning (1/day, pound the ground to create a 60ft shockwave that forces up to 45 hit points worth of enemies to save vs. spell or be stunned for 1d4 rounds). Additionally, a dwarf wielder can throw the hammer 150 feet as a ranged attack 3/day, with it returning each time it is thrown. However, it bears a minor curse and inflicts severe agoraphobia on the bearer, causig them to take a -2 penalty when not fighting in an enclosed space or at night.
When 2nd edition came along and Whelm reappeared in "Return to White Plume Mountain", it hadn't changed much. It was still a sentient +3 (+5 for dwarves) magic hammer that retained its former traits, but the precise mechanics had been tweaked. Now its Int was 14 and its Ego was 20, and it would try to force its wielder to go goblin-hunting if they failed to kill at least one goblinoid, giant or troll a month. It could still be thrown 150 feet three times per day and unleash a stunning 60ft shockwave (up to 7 HD of enemies now had to save vs. spell or be stunned for 1d4 rounds), but these powers weren't racial restricted. Its sensory range to detect gold, gems and goblinoids was now clarified to be 60 feet. It also gained a new power; on a critical hit, a Large or bigger creature would take +20 damage and a Medium or smaller creature would be hit with a Disintegrate spell. However, its agoraphobia (now specified as a penalty to attack rolls, saving throws, and proficiency checks) was more severed. You see, for each consecutive 24-hour period without spending at least 8 hours inside or underground, the penalty increased by a further -1, maxing out at a -5 penalty.
Like all of the White Mountain Weapons, Whelm received its 3.5 update in "White Plume Mountain Revisited", which is now all but impossible to find due to the collapse of the old WoTC internet archives. Luckily, /tg/ gets shit done and so you cn find it here.
As with the other three White Plume Weapons, Whelm is treated as a Weapon of Legacy in 3.5, although it's honestly the wimpiest of them all; not only does it only reach up to level 16, it only has two Legacy Rituals: Against The Giants (knowingly and willingly enter battle against a giant-type creature in an encounter where the EL exceeds your party level by at least 1) and Against The Goblins (slay a group of goblinoids with at least 30 HD collectively, during which you defeat a hostile goblinoid with a CR at least equal to your character level).
This version of Whelm can oly be used by a Dwarf character with a BAB of +3 and Weapon Proficiency (Warhammer). Starting its existence as a +1 warhammer, it upgrades to a +1 giant bane warhammer at 6th level, a +1 giant & goblin bane warhammer at 11th level, and then increasing in potency to +2 at level 13 and +3 at level 16. Its initial special ability at level 5 is "Sense Giants", which functions as a permanent Detect Evil spell that detects giant-type creatures within 60 feet. At 8th level, it can cast Locate Objects 3/day, and gains "Sense Goblinoids", which is just like "Sense Giants", but for goblin-kin. Finally, at 10th level, it becomes a sentient item with a 60ft sensory range (hearing and darkvision), Int 16, Wis 16, Cha 10, and Ego 14, increasing to 15 at 14th level and to 16 at 16th level.
Because of Whelm's long history with Ctenmiir, it appeared as a Paragon tier artifact weapon in 4th edition's "Open Grave: Secrets of the Undead" sourcebook. This +3 magic warhammer has increased critical hit damage against creatures bigger than Medium sized (+3d10 instead of +3d6), grants +2 to Perception checks, can be used as a Heavy Thrown weapon with range 5/10 due to teleporting back to the wielder's hand, and grants 3 Paladin powers as bonus attacks; Valiant Strike, Thunder Smite and Bloodied Retribution. Needless to say, it prefers a dwarven wielder (+2 Concordance), but so long as you keep killing goblins, trolls and giants, it'll be happy (+1 Concordance on any day you kill one). On the other hand, going without at least one such kill a week will tick it off (-1 Concordance), and it will be extremely pissed if taken up by a goblin, troll or giant (-5 Concordance). When Satisfied, it boosts its Perception bonus to +3 and grants the Paladin's Turn The Tide Daily Power. When Happy, it increases to a +4 warhammer (crit damage goes up to +4d6/+4d10), grants +2 Initiative, and gives you the Fighter's Dragon's Fangs Daily power. When Unsatisfied, it inflicts a -2 penalty to Initiative and to all attack rolls against creatures that aren't goblins, trolls or giants - and this applies even if you're not wielding Whelm. When truly Angered, it drops in power to a mere +2 weapon and the attack roll penalty increases to -5. When it moves on, if satisfied, it leaves a +3 warhammer as a thank you.
The most recent version of Whelm showed up in the Dungeon Master's Guide for D&D 5e. This artifact-tier +3 warhammer can only be used by a dwarf. It still imposes its traditional agoraphobia, giving you Disadvantage on attack rolls, saving throws and ability checks so long as you can see the daytime sky. It can be thrown 20 feet, which causes it to inflict +1d8 bludgeoning damage on a hit (+2d8 on a giant), and can be used to create a Shockwave attack once per day. This forces a DC 15 Constitution save for each creature on the ground of your choice within 60 feet, or else they're Stunned for 1 minute or until they make their save. Its Supernatural Awareness makes the wielder automatically aware of secret/concealed doors within 30 feet, and lets them cast either Detect Evil & Good or Locate Objects 1/day. Finally, it's a sentient weapon; Int 15, Wis 12, Cha 15, hearing and darkvision to 120 feet, communicates telepathically, speaks Dwarvish, Giant and Goblin.