I use them all the time. In my game world, magic is a rare, unpredictable force...not just another resource or energy to be harvested. Most, if not all, magic items have some sort of drawback.
Some of my favorites:
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scythe +5 that works normally until it scores a critical hit. On a crit, it splits the damage between its target and its wielder (ouch).
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morningstar +1 that gives its weilder the ability to rage like a barbarian, once per day. The trouble is, the endorphins and "rush" created by this artifical rage are highly addictive, and each time it is used in this manner, the wielder can become addicted to it (Fort DC 20 negates). Characters who are addicted to the rage become nonproficient with all other weapons, including other morningstars.
A
sling +2 that launches "returning" stones...which sounds like a good thing, but it isn't. On a miss, the returning stone flies back and attacks the one who threw it, using the same attack bonus. Sort of like a low-grade
backbiter spear.
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ring of invisibility that works like normal, but if it is used more than once per day, the character begins to fade away (-1 Strength per hour, character dies and immediately becomes a shadow when Strength = 0.)
A super-powerful
potion of healing that cures 20 points of damage automatically (no need to roll), but also causes nausea for 4 hours (Fort DC 12 negates.)
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cape of the mounteback that works normally, except that the character wearing it always leaves a random item behind when he/she teleports. This was used to great effect when the character was trying to impress the queen by putting on a little "magic show" after dinner, and when he DD'd across the room he accidentally left his clothing behind.
The queen was so impressed (and amused), she gave him new robes fit for a king.
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