Wondrous Item, Very Rare, Requires attunement
While this pale lavender ellipsoid orbits your head, you can use your reaction to cancel a spell of 4th level or lower cast by a creature you can see and targeting only you.
Once the stone has canceled 20 levels of spells, it burns out and turns a dull gray, losing all its magic. If you are targeted by a spell whose level is higher than the number of spell levels the stone has left, the stone can't cancel it.