Here, I will talk about how to make a cursed item that will have an effect on your party. Here it is!

Steps

1. Make an item called something, whatever you want if you want to be sneaky or something, then make a common event called "Cursed Item" (#""(If you have multiple cursed items)), then make another item that is the cure to it. For example, you could make the cursed item called "Awesome Cure" or something.
2. In the common event:
3. Make a conditional branch that says "If item () is possesed...", where () is the item that heals the cursed item.
4. And under "If item () is possesed" make it erase the cursed item.
5. Still under it, make it give back whatever it took. (the lives, bla bla bla)(see Step 6)
6. Under the other one, make it do something bad. (health, weapon, levels, a party member, etc.)
7. Go to the item "Awesome Cure" or something and make the common event "Cursed Item." Make the item available in battle and from the menu, make it un-eatable, make it the price you want (if any), put everything at 0, and make the accuracy 100%.

There you go. You now have a cursed item and a item to cure it.
You don't have to credit me, but it would be nice.
Your Welcome!