A Sword Called Clarity

Clarity is a human-forged longsword, but close examination reveals it uses elven techniques to entwine two blades into one.  

This well-made long sword has the words FIAT LUX along one side of the entwined blade and the word VERITAS on the other.  These are the command words for two related, yet distinct powers.

Sword of Hearth and Home by Chris Rahn, Magic the Gathering

By uttering FIAT LUX, the sword becomes the center of a double-strength Daylight spell, extending out 120' in each direction, and moving with the swordbearer.

Speaking the word VERITAS causes the wielder's eyes to glow a solid blue.  These glowing eyes function as Truesight, True Seeing, Arcane Sight, detect alignments by the auras of varying colors around each being, and can see into the Ethereal and Astral planes; basically, the wielder gets Wizard Vision.  

Depending on what they see, however, can drive the viewer temporarily mad, stunning them into inaction as they see everything as it truly is.  Mechanically, this is a Wisdom save at DC 15 (or higher depending on what the DM knows is actually there).  Failure to save means the viewer is stunned for a round.  This save is made each round until it is made, then the glow in the eyes fades away, returning the eyes to normal, but the PC changed.

While stunned, the PC just stands there, defenseless.  Successful strikes against the stunned viewer allow an additional saving throw.  

This experience leaves the viewer far more knowledgeable, but with a level of exhaustion.  At the DM's discretion, there may be a small chance for a permanent increase (or loss) of Wisdom for the PC.

A Sword Called Spellbreaker

Spellbreaker is an ancient bronze short sword, forged for use by Magekillers during the Mage Wars.  Its crafters did their job too well, however, as once attuned to Spellbreaker, its wielder is immune to ALL spells that target them - for good or ill.  Attuning requires a permanent loss of 1 point of Charisma and lasts until someone else attunes to the blade.

Potions still work, but spells cast from beings, scrolls, wands, and some spell traps do not.  Area effect spells fail if wielder is the targeted point, but splash damage from such spells works normally, requiring saves as per the spell.  For example, a Fireball thrown at Spellbreaker's wielder fails to go off, but a Fireball targeting the ground next to the wielder goes off as normal.

Spellbreaker is a +2 short sword that can Dispel Magic on the target on a successful strike (useful for piercing magical defenses).  1/day (or 1/long rest), the wielder can create an Anti-Magic Field, centered on themself.  If the wielder holds their action, they can attempt to use Spell Cleaving - effectively cutting a spell off in midair; spells have an effective AC of 10+their level.  On a critical hit, the Spell Cleaving instead sends the spell back at its caster.

From the Magic card Bronze Sword, artist Kev Walker

A Sword Called Mistcutter

Mistcutter is a fine bastard sword with a repeating helix pattern running along much of the blade.  It glows with a bluish light under normal circumstances but can flare into brightness as per Daylight when needed (it's call or it's wielders).  Mistcutter exists to cut through lies and deceit, leaving only Truth.

From the Magic card Valkyrie's Sword, art by Aaron Miller

As such, Mistcutter is considered True Neutral in alignment, for as long as the truth is made known, it cares not one jot nor tittle about the results of such revelations.  As such, it prefers Lawful and Good aligned wielders, as those beings tend to be more honest than those with a Chaotic and Evil bent.

The being that is the source of Mistcutter's sentience was a Human barrister and judge, renown for his impartiality and single-minded pursuit of the truth.  One tale is that he condemned himself and his family to death because of this sticking to the truth.  Grandfather Favarro was watching from afar, having orchestrated the entire series of lies that eventually led to the grand state execution of the judge and his bloodline.  

At the moment of death, Grandfather Favarro snatched the judge's soul through foul magics and channeled that single-minded pursuit of truth into the sword now called Mistcutter.

Whomever grasps Mistcutter by the hilt hears its voice* in his head (speaking with authority and often questioning everything - perhaps it mansplains), and if necessary, aloud with a voice loud enough to force a random encounter roll.  This is because Mistcutter has both Telepathy and Speech, with the gift of Tongues, to be certain there is no misunderstanding.

The voice demands, 'do you agree to seek the truth, the whole truth, and nothing but the truth?'  Answering 'no' results in Mistcutter writhing and twisting in the wielder's grasp, dealing 3d4** psychic damage each round until released.  Answering 'yes,' however, begins the attuning process. 

Attuning results in Mistcutter purging all existing illusions and shapechanges currently upon its wielder.  Furthermore, it then uses its telepathy and Detect Thoughts to interrogate the prospective wielder, asking questions about lies and truth and such.  (A wise DM would have such questions ready before the session where Mistcutter is likely to see play).  If the prospective wielder passes muster, then Mistcutter attunes completely.

As long as Mistcutter approves of its wielder, the wielder has Truesight.  

Truesight - 120'

A monster with truesight can, out to a specific range, see in normal and magical darkness, see invisibile creatures and objects, automatically detect visual illusions and succeed on saving throws against them, and perceive the original form of a shapechanger or a creature that is transformed by magic.  Furthermore, the monster can see into the Ethereal Plane within the same range. 

Swords are intended for combat, and as such, Mistcutter provides a +3 to hit and +2 to damage. In addition, a successful hit from Mistcutter dispels any Illusions cloaking the target (as per Dispel Magic, but only against Illusions) as well as forcing shapeshifters and polymorphed/wild shaped beings into their natural forms (whatever that may be).  

But not everything is immediately beneficial to a wielder.  At all times, Mistcutter's wielder is under a Zone of Truth (DC 18).  Mistcutter (and sometimes its wielder) can extend the zone up to 120' feet.  Another potential drawback is that the attuned wielder cannot shapechange or have an illusion cast upon them.  Such things just fail outright, although Mistcutter is aware of the attempt, and woe to the wielder if they are the cause of it!

Like most sentient items, Mistcutter can activate, deactivate, or refuse to activate most of its powers as it sees fit. While not given to whimsy, Mistcutter will pout and go dormant if proven wrong. The only powers it cannot shut off are the +3/+3 to attacks and Dispelling Illusions on a successful hit.

If the wielder knowingly lies, Mistcutter deals 3d4** psychic damage to them.  Should lying be a regular occurrence, Mistcutter will attempt to dominate its wielder, forcing the wielder to pass the sword to a more worthy being.

Lastly, Mistcutter will first urge, then attempt to dominate, its wielder to reveal any illusions and lies they come across.  As might be imagined, Mistcutter and rogues tend to not get along.

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Mistcutter is a dangerous tool for those that practice deceit, but for the honest adventurers out there, it is a potent tool for combatting all sorts of typical villainy and thwarting DM plans.

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* the voice idea stems from Telecanter's Receding Rules DM Aids, specifically the Voices document.  So much goodness among those aids you should consider porting into your games.

**3d4 doesn't seem like much, until one takes into account cascading damage, which is one of my houserules.  There is a saying that the truth hurts, but it ain't got nothing when a lie ends up causing 40-50 damage.  Now that is a killer migraine!

A Sword Called Honor

Honor.

Honor's sentience is provided by the essence of a Marut.  As such, Honor has rather strict definitions of what is, and more importantly, what isn't, honorable behavior. Wielders that are honorable by its definition gain all sorts of benefits, while those that act in a dishonorable fashion suffer penalties.

Presume the LEGO person is 6 feet (about 2 meters) tall.

Its hilt is wrapped with unicorn-leather and the weapon itself is forged from a magical alloy of moonsilver, cold iron, orichalcum, mithril, heartwood, onyx, and steel, Honor can slice through all material-based resistances, presuming it connects, of course.  To assist in this endeavor, honorable wielders using Honor as their weapon gain Advantage on attacks.

In addition to Advantage on attacks, critical hits trigger a Thunderwave spell upon the target.

Honor also provides access to several abilities stemming from its Marut essence: Air Walk, Dimension Door, Locate Creature, True Seeing, and Plane Shift.  While the sword's wielder can activate these abilities, Honor will also use them in pursuit of the 'honorable' solution, or to prevent a dishonorable situation.

Below are some ideas regarding Honor's thinking.

Examples of what Honor considers honorable behavior:

• accepting a challenge to a one-on-one duel
• issuing a challenge for a one-on-one duel
• sacrificing self for others, typically via combat
• announcing oneself before attacking
• making a promise, vow, or taking an oath
• keeping a promise, vow, or oath
• accepting the surrender of enemies

Examples of what Honor considers dishonorable behavior:

• surrendering to save one's own life
• not accepting a challenge to a one-on-one duel
• murdering prisoners that had surrendered
• murdering beings that cannot defend themselves
• putting self before others
• not attempting to rescue comrades-in-arms during a battle
• retreating from a fight once started (but not avoiding a fight entirely)
• attacking from behind or from ambush
• the use of poison
• breaking a promise or vow or oath
• breaking any personal taboos (Honor knows)
• using any of Honor's abilities to leave a fight - major infraction
• using any of Honor's abilities to 'cheat' a fight - major infraction

Honor is capable of speech, but doesn't speak much.  When it does speak, it is either to answer a direct question asked of it, to warn the wielder of a potential dishonorable act, or to issue a challenge to something mighty in order to give its wielder a chance to redeem their honor.  This challenge is always in a language the mighty thing can understand - and so can the wielder.  

It always speaks in a loud, clear, emotionless voice.  Its challenges are more booming than just plain loud.

For minor infractions of dishonor, Honor's wielder attacks at Disadvantage.  For larger infractions, Honor will challenge creatures or beings to single combat, and that entire fight the wielder is at Disadvantage.  Honor may instead demand some form of service from the wielder to redeem itself.  Once redeemed in Honor's eyes, attacks are at Advantage and powers become available again.

In extreme circumstances, Honor will attempt to dominate a dishonorable wielder in order to have them go somewhere private and commit seppuku. At this point, the wielder is dead and their honor redeemed.

As such, this is how Honor is normally discovered - in the belly of a kneeling corpse or skeleton in some out of the way location. 

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DM Notes: Honor as a whole is a slippery concept that walks a fine line between vainglory and pride.  

For inspiration, look at real world honor-bound cultures for ideas.  

Alternatively (or additionally), there are tables in the 1e Oriental Adventures, the CMG supplement, the 3.5 SRD ruleset, Pendragon (any edition), Hackmaster, and other systems and games.  Just be sure to let the PLAYERS know what the sentient blade finds honorable and dishonorable... if they think to ask it.  If not, trial by error is a method.