Magic Items with a twist (evil twist)

My players are constantly wanting magic items to the point of annoying. But then of course they get way to powerful.

So, I decided to give them magic items with a twist.

Example:

a +1 ring of protection with all the standard feature, but when they have a successful attack roll, the ring cast Faerie Fire on the wearer.

a Boots of Elvinkind, they do everything they should, but they reduce the players movement by 5 ft.

That sort of thing. I need ideas for magic items and ways to nerf them.