I recently stumbled upon the RPG Blog Carnival and was intrigued by this month's topic: Curses! Cursed Items, Spells, Campaign Stories (hosted at Roleplaying Tips). It's a fun topic from the game master's perspective so I thought I'd take part.
The intrinsic value of a magic item comes down to balancing its benefits against its costs. Cursed items that hinder or, worse, try to kill a character don't have much value and it's an easy call for the party to ditch it at their earliest convenience. However, to me, the best cursed items are ones that have a beneficial aspect to them as well. Suddenly, the players need to determine if they can deal with the difficulties of carrying the item with them (at least temporarily) in order to benefit from that item's more benevolent features.
As part of a creative exercise, I've created a list of 20 qualities that a GM might give a magic weapon that could render it cursed. Since they come from a brainstorming session, these qualities should be functional, but some may need a little refining to achieve better game balance and clarity. Not every quality is entirely negative, but all have some sort of cost associated with them. In some cases, it may be more dramatic to withhold the malevolent effects of the curse from the players, especially in the case where the effect is not immediately evident.
Bloodied. While you are holding this weapon, if you do not deal damage to a living creature before the end of your turn, you use this weapon to deal damage to yourself equal to it's average damage value. Do not apply your Strength modifier or other damage dice to this damage.
Blinding. A blinding weapon is made of highly polished metal that is exceptional at reflecting light. Its effects can only occur in areas of bright light. When you confirm a critical hit with this weapon, you may choose to deal normal damage and blind your opponent for 1d4 rounds. However, if your attack roll is ever a natural 1, you automatically blind yourself for 1d4 rounds.
Booming. This weapon issues a thunderous boom when it strikes true. When you score a critical hit with an attack from this weapon, the target and all creatures adjacent to it are deafened for 1d4 rounds.
Clumsy. If you miss with an attack with this weapon, you must succeed at a DC 12 Dexterity (acrobatics) check or fall prone.
Decapitating. All attacks that threaten a critical hit against you are automatically confirmed. If you die as a result of a critical hit, the blow removes your head.
Dulled. This weapon only deals bludgeoning damage equal to your Strength modifier.
Electrified. When drawn, veins of energy begin to dance along the blade and hilt as this weapon crackles with electricity. When you hit with an attack using this magic weapon, the target takes an extra 1d6 lightning damage. In addition, while you hold the sword, you take 3 points of lightning damage each round.
Exhausting. This weapon requires significantly more effort to wield in battle, although its blow tend to be much more devastating. All hits with this weapon threaten critical hits, but if you miss with an attack with this weapon, you gain 1 level of exhaustion.
Gaseous. This weapon carries with it an aura of noxious fumes. A powerful strike causes it to expel a poisonous gas cloud. When you hit with an attack with this weapon, the target must succeed at a DC 12 Constitution saving throw or become poisoned for 1 round. If you ever roll a natural 1, you accidently inhale the fumes and are poisoned for 1d4 rounds.
Isolating. While you are holding this weapon, allies cannot approach within 10 feet of you. Any ally that is already within 10 feet of you when you pick up the weapon cannot move any closer.
Leeching. This weapon draws upon the life force of your allies to keep you safe. When you suffer hit point damage, you take no damage; instead, the closest ally within 30 feet of you takes an amount of necrotic damage equal to the damage you would have sustained. This damage cannot be reduced in any way. If there is no ally within 30 feet of you at the time you take the damage, you suffer the damage normally.
Lodestone. For each attack you make with any weapon other than this one, your speed is reduced by 5 feet. This reduction disappears once you make an attack with this weapon against a target that is within your reach.
Merciless. You have advantage on attacks made against any creature with less than one half of its maximum hit points, but attacks against you gain advantage if you have less than one half your maximum hit points.
Murderous. If you miss with an attack with this weapon, you strike yourself and deal damage as normal. On a roll of a natural 1, you score a critical hit against yourself.
Offensive. There is something about you having this weapon that other creatures find insulting or offensive. Creatures of one specific type (i.e. beast, fey, fiend, undead, etc.) chose to attack you over other targets.
Seppuku. At the end of any combat in which you did not adhere to the weapon’s honor, you must succeed at a DC 15 Charisma saving throw or impale yourself upon this weapon. If you fail the saving throw, you deal maximum critical damage to yourself. Roll on the table below do determine the weapon’s honor.
1 – Deliver the killing blow to at least one creature.
2 – Do not make an attack with advantage.
3 – All allies are alive at the end of combat (they may be unconscious).
4 – Do not attack a non-spellcaster so long as an enemy spellcaster is present.
Spell Loathing. When you are affected by a spell (even if you passed the saving throw), you have disadvantage on your attacks for a number of rounds equal to the level of the spell slot that was used to cast the spell.
Vengeful. Each time you deliver the killing blow to a living creature while attuned to it, you suffer a cumulative 1 point of psychic damage.
Xenophobic. You have disadvantage when attacking creatures of a specific type (i.e. beast, fey, fiend, undead, etc.). In addition, you become frightened of any creature of that type that causes damage to you.