I infrequently post about magic items unique to my games (see Magic Item under labels) but I rarely talk about swords, especially powerful ones.
But I have them! Here are a few:
Seaward Weapons
A almost 40 year old AD&D 1e campaign
Mor Altach: Long sword of Wounding. +1 to hit (only). Intelligence of 12-14, Chaotic Good. Speaks a few languages. Can be used by barbarians. Doubles the chances of a barbarian that wields it to go berserk. Can emit light as a lantern (this can be varied or turned off). The following special powers are 'secret' and must be learned through use and experience.
Once a person that wields it as their primary weapon has leveled up twice it acts as a Ring of Free Action. Once its wielder has used it to kill a Devil it is +4 to hit devils. Once its wielder has fallen 21' or more while holding it, it acts as a Ring of Feather Fall. Once a person that wields it as a primary weapon has leveled up 6 levels it becomes +4 to hit and damage (if the Devil ability is activated, it is a total of +7 to hit vs devils). Once its wielder has failed a Petrification save while holding it, it grants a +4 on all saves vs Petrification.
Rupert's Blade: +3 broad sword. Wielder can boost their strength to 18/00 once a day - this lasts 5 rounds. Wielder also has a +2 save vs poison while holding it. Anyone wielding Rupert's Blade can instantly recognize an undead on viewing by type and kind (i.e., a master vampire, a frost zombie, etc.) and are immune to characteristic loss, level drain, etc. from any undead they can see.
Lawbringer: +4 longsword. LG, Int 13, can communicate with emotions and vague imagery. The wielder can Detect Evil as a paladin. It is a holy weapon: in the hands of a paladin it is +6 and doubles the range of the paladin's Detect Evil ability and grants all powers of a holy sword as listed in the PHB. Lawbringer cannot be Cancelled, Disjoined, or otherwise disenchanted unless the being doing so is a Lawful Good cleric of 18th or higher level.
Thresher: Two-handed sword. +3 to hit, +6 to damage. It doubles the number of attacks versus low hit dice creatures to a maximum of 30 attacks/round.
Drachenbane: +3 two-handed sword. It does double damage to all drakes, dragons, and such creatures and versus chromatic dragons it does increased die as well (i.e., versus a dragon turtle it would do 6d6, but against a red dragon it would do 6d8).
Blackstone Weapons
From my 12+ year old 2e campaign.
The Seven- seven two handers of unmatched power. The ones seen by players-
Gatekeeper: +4, +5 versus extra-planar/summoned creatures. Once a month it can automatically permanently seal any Gate by touch. Wielder has a +1 on all saves, +2 versus Summoned or extra-planar creatures.
The Paradigm: +7. It's pluses do not get reduced by planar travel, etc.
Staredge: +4 to hit only. On a natural 18 or 19 to hit it does double damage. On a natural 20 it does double damage and will sever an extremity as a Sword of Sharpness.
Swords that are not of the Seven.
Death's Sting: +7 long sword, does double damage. (Destroyed).
Magekiller: +3, +5 versus arcane spellcasters or creatures with spell-like powers that mimic arcane spells. Grants anyone holding or carrying it a +2 on all saves versus spells or magic items and reduces damage from all magical attacks by -1 h.p. per die (minimum of 1). When in-hand it gives it wielder a 50% Magic Resistance. While intelligent and strong-willed, it rarely communicates. It can Detect Magic within 10' (automatic), Detect Arcane Spellcasters (and if they are good, neutral, or evil) within 60' (automatic), and can Dispel Magic at 18th level once a day. It will pass along what it senses to its wielder telepathically.
Magekiller was forged to slay evil arcane spellcasters. It grants an additional +2 to save/-1 h.p. per die against spells cast by arcane spellcasters.
Once per week Magekiller can act as a Rod of Cancellation; the sword will decide when this power is used.
