These weapon attachments can be affixed only to mundane and +X weapons. A weapon can only have one attachment at a time. Applying an attachment, or swapping one out (or transferring from one weapon to another), takes an hour. This time can be combined with a short rest. The DM is free to adjudicate that an attachment is integral to a weapon and either cannot be detached, would destroy the source weapon, or requires special tools or skills. For example, it might not make sense to transfer a Sturdy Construction attachment from a dagger, or perhaps a runeword is not easily transferred without the aid of a trained rune-scribe.

If any effect caused by an attachment requires a saving throw, its DC is equal to 8 + your proficiency bonus + the stat modifier used to attack with the weapon + any magic bonus the weapon has. For example, if a level 5 character with a Strength of 18 attacks and crits with a +1 Maul with a Counterweight the DC for the Stun effect is 8+3+4+1=16.

Acquiring attachments

Attachments come from various places. Some can be found as loot, either alone or already affixed to weapons, other are sold by merchants or must be crafted. Some attachments might have magical components, but this does not make a mundane weapon into a magical one.

The following table is a general guide on how these items might be acquired. The Loot CR column might either be where the items are acquired as drops, or where the most difficult component is found, which could be combined with a gold cost for a artisan crafter's fee.

Rarity	Price range	Loot CR	Crafting Note	Power Note
Common	50-100gp	0-4	Easily made by even a modestly skilled artisan with common materials	Small, situational benefits that make a weapon slightly more unique. Rarely magical.
Uncommon	100-1000gp	5-8	Requires at least one more costly component and/or a skilled artisan	These benefits are useful most of the time. Can be magical or just well-crafted.
Rare	1000-5000gp	9-12	Requires a component that is not easily purchased and/or a very specialized artisan	Usually a bit of magic involved. On the powerlevel of an Uncommon weapon, or part of a feat.
Very Rare	5000-20000gp	13-16	Requires multiple, possibly extraplanar, components and a master craftsman	Useful effects that you could find on a Rare weapon or a half-feat.
Legendary	20000-??gp	17+	Requires scouring the multiverse for components and those that can craft it	No limit on the power level, but probably atleast as good as a very rare weapon or a full feat.

Improving mundane treasure

You can roll on this table to determine the attachment quality for a mundane or +x weapon. Add the CR of the treasure source to the d20 roll. As an example: the party defeat an Adult Green Dragon (CR 15), and there is a +2 Rapier in its hoard (determined either by rolling, or otherwise). To make this item stand out a bit more, you roll on the following table and get a 14, for a total of 29. A rare attachment to the Rapier might be a Spell Focus Gem - perhaps the weapon belonged to a Bladesinger Wizard that was defeated by the dragon. Not every item needs an attachment, but they can help make otherwise anonymous treasure stand out.

d20	Attachment
0-12	Any common
13-25	Any uncommon
26-35	Any rare
35-39	Any very rare
40+	Any legendary

If you want to make your own attachments, consider why it isn't a regular magic weapon. For example, an effect that could only be applied to a whip is probably best suited as a magic weapon. A well designed attachment is useful for a variety of classes and weapon types.

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Attachments and bounded accuracy

Since none of these require attunement, and in fact may replace an attunement slot that was otherwise used for a magic weapon, you might be hesitant to add these to your game. Consider restricting it to only the common and uncommon attachments, which should not affect player power too much. You could also rule that a weapon with an attachment (either with some minimum rarity or all of them) require attunement.

Sturdy Construction

Any Light, common

The weapon's damage die becomes one size bigger (for example, a dagger goes from d4 to d6), but it is no longer Light.

Spiked Head

Any Bludgeoning, common

Critical strikes with this weapon deals an extra weapon die of piercing damage. This die is not doubled.

Stabilizers

Any Thrown, common

Removes the penalty for attacking at long range with this weapon.

Beak Hook

Any Reach, common

On a critical hit with this weapon, the target must succeed on a Dexterity saving throw or be knocked Prone.

Jagged Edge

Any Slashing, common

On a critical hit with this weapon, the target must succeed on a Dexterity saving throw or become Restrained until the end of your next turn.

Bipod

Any crossbow, firearm, or blowgun, common

Negates disadvantage from attacking while Prone with this weapon.

Crafting component suggestions

All the components listed here are a suggestion of what could be required to craft an attachment. You are always free to award them however you like.

Eternal Fire-tube

Any crossbow, bow, firearm, or blowgun, uncommon

Using a bonus action, you can toggle the light on and off. When on, it sheds bright light in a 30-foot cone, and dim light for an additional 30 feet.

Possible crafting components: 250 gp diamond, Fire Elemental essence

Beamsight

Any crossbow, bow, firearm, or blowgun, uncommon

Projects a small point of light at the point of aim which negates the disadvantage from attacking in melee range with this weapon.

Possible crafting components: Catoblepas eye, Crystal Golem core

Barbed Hooks

Any Piercing melee, uncommon

You can use this weapon to make a Grappling attack. If you succeed, you deal the normal damage for the attack. If you have a creature grappled in this way, you cannot attack with the weapon.

Magnifying Eyepiece

Any crossbow, bow, firearm, or blowgun, rare

Negates disadvantage from attacking at long range with this weapon.

Possible crafting components: Water Elemental Myrmidon Crystal

High-power Scope with Bipod

Any crossbow, firearm, or blowgun, very rare

Negates disadvantage from attacking at long range with this weapon. Additionally, while prone, you have advantage on attacks within your short range.

Possible crafting components: Adult Sapphire Dragon eye, Iron Golem digits, Mummy Lord amulet

Low-power Night-vision Scope

Any crossbow, bow, firearm, or blowgun, rare

Grants 60 ft of darkvision while holding this weapon. You cannot see colors through the scope, only shades of green.

Possible crafting components: Piece of translucent jade, blessed by a deity of the night, such as Selûne or Caldir

Ashen Rider Femur

Any crossbow, bow, firearm, or blowgun, very rare

The residual aura of silence on this hollowed-out femur negates any noise made from a projectile that passes through it. If you make a ranged attack with this weapon while hidden, your position is not revealed.

Composite Limbs

Any bow, uncommon

You can use strength instead of dexterity to attack with this weapon.

Lizard Leather Handle

Any, uncommon

The weapon cannot be disarmed from you unless you are Incapacitated.

Suggested crafting components: Tyrannosaurus Rex leather

Poison Tip

Any Piercing, uncommon

When you hit an enemy with this weapon, you can force them to make a Constitution saving throw. On a failure, they take 2d8 poison damage and become poisoned until the end of your next turn. You must finish a long rest before you can do so again.

Possible crafting components: Hellwasp stinger, Hydra poison sac

Vine Bowstring

Any bow or crossbow, uncommon

While you are holding this weapon, you can cast the Grasping Vine and Entangle spells. When you cast either one, you must finish a long rest before you can do it again.

Possible crafting components: Assassin Vines, Treant beard

Counterweight

Any Bludgeoning, uncommon

On a critical hit with this weapon, the target must succeed on a Constitution saving throw or become Stunned until the end of your next turn.

Possible crafting components: Ankylosaurus tail, Earth Elemental boulder

Silver Inlay

Any mundane melee, uncommon

The weapon counts as magical for the purpose of overcoming resistance to non-magical damage.

Adamantine Edging

Any melee, uncommon

This weapon gains the Siege property, doubling damage done to structures and objects.

Concealed Thigh Scabbard

Any light, uncommon

With this scabbard the weapon is stored closed to your body. You have advantage on any Stealth or Sleight of Hand checks to conceal it.

Quickdraw Scabbard

Any finesse, rare

With this scabbard, your weapon is always ready for action. You can add your proficiency bonus to initiative rolls.

Basket Hilt

Any Finesse, uncommon

If you wield this weapon in one hand while not wielding another weapon or shield, you gain +1 AC.

Vampire Fang Tip

Any Piercing, rare

When you reduce a creature to 0 hp with this weapon, you gain 2d6 temporary hit points.

Eladrin's Bouquet

Any Thrown, rare

After throwing and hitting with this weapon, you can teleport to the impact site (either a location or next to a creature). You emerge at the location, holding the weapon. Once you do this, you need to finish a long rest before you can do it again.

Suggested crafting components: A flower from each type of Eladrin

Scintillating Inlay

Any melee, rare

You can cast the Absorb Elements spell while you are wielding this weapon. The extra damage is increased to 3d6. Once you cast the spell, you need to finish a long rest before you can do so again.

Possible crafting components: Flail Snail shell fragments

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Runes

Runes carry innate magical power. Working with these powerful words require special care. You might not be able to transfer a runeword as easily as a pommel gem. It might be as easy as an Arcana check, or as complex as finding the legendary rune-master who wrought it in the halls of the afterlife.

Longer runewords are generally more powerful, but this is not absolute. All the runes have several meanings, and deciphering the meaning of a runeword might be involve interpreting several layers of allegoric references.

Runeword: Light (sg)

Any, common

The weapon emits dim light in a 10-foot radius.

Runeword: Time (rdb)

Any, uncommon

The runes in this inscription change over time, always indicating the current hour of the day. This only functions on the material plane.

Runeword: Return (ro)

Any Thrown, rare

After throwing this weapon, it returns to your hand with a flash of light.

Runeword: Fury (uxg)

Any, rare

This weapon also deals a critical hit on a 19 on the d20.

Runeword: Luck (ogfm)

Any, very rare

You gain a +1 bonus to ability checks and saving throws while holding this weapon.

Runeword: Arcana (gdsixu)

Any, very rare

You can use your spellcasting ability to attack with this weapon. It also functions as an spellcasting focus for you.

Luxite Crystal Emitter

Any melee, legendary

This replaces the blade or head of the weapon. While holding the weapon, you can cause a beam of radiant light to emerge which takes the shape of the blade or head. This emits bright light in a 15-foot radius and dim light for an additional 15 feet. The light is sunlight. You can use an action to make the radiant head disappear.

While active, the weapon gains a +1 magical bonus. If it already has a bonus, it is increased by +1, but not above +2. Attacks with the weapon deal radiant damage instead of the normal kind for the weapon. An undead creature hit by the weapon takes an extra 1d8 radiant damage.

If you are holding the weapon and it is active, you can use and action to cast Crusader's Mantle. Once you do so, you can't do it again until you finish a long rest.

Elemental Amulet

Any, very rare

A hanging magical trinket that imbues the weapon with a part of the elemental power it possesses. The weapon deals an extra 1d4 damage of the specified type on hit. If the weapon is wielded with both hands, the damage increases to 1d6.

It is possible to acquire even more powerful versions of these trinkets, which also grant resistance to the relevant damage type. Those Elemental Amulets are Legendary instead of Very Rare.

d10	Item	Source	Damage type
1	Efreeti Firesilk Ribbons	Efreeti	Fire
2	Pristine White Dragon Fang	Adult White Dragon	Cold
3	Inscribed Black Dragon Scale	Adult White Dragon	Acid
4	Erinyes Poison Sac	Erinyes	Poison
5	Djinni's Carved Amber Gem	Djinni	Thunder
6	Elder Brain Tentacle Tip	Elder Brain	Psychic
7	Storm Giant's Beard Tassel	Storm Giant	Lightning
8	Goristro Horn Spike	Goristro	Force
9	Mummy Lord Talisman	Mummy Lord	Necrotic
10	Sphinx Feather	Androsphinx	Radiant

Some of these might be given willingly by the creatures as a reward for a service rendered.

Spell Gem

Any, rare

This weapon can be used as a spell casting focus.

Possible crafting components: depends on the source of magic. A cleric might need a miniature statue of their deity, a wizard a rare gem etc.