This item can be used to enhance skill, but at a cost.

A crystal that should have been hidden from mortal hands has been rediscovered. It's power is that it can boost the ability (like a spell or action) of someone drawing from the crystal. It disintegrates after one use.

While the crystal gives power, I want it to take something away or give some aliment to the user, without being either inconsequential or completely overbearing that the choice is easy to not use the crystals.

I'm just not sure where to start here to make them enticing but dangerous. I appreciate any help to give here!