A silver ring, set with a blue tiger eye gem. The inside edge of the ring shows the alphabet of the native language of the bearer. Once attuned, the bearer of this ring gains the ability to alter one spell that they can already cast, by changing one letter of the spell. For example, a spell-caster may change "Wall of force", to instead make a "Ball of force", or "Cone of cold" into "Cone of mold".
The effect of the new spell is negotiable with your DM, and once the ring is used in this way, it cannot be used again until you have taken a long rest.