Ioun Stone of Absorption

While this pale yellow cube 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 dull gray,
losing its magic. If you are targeted by a spell
whose level is higher than the number of spells
the stone has left, the stone can't cancel it.
Surprisingly, it was an Undergrad student who
first discovered the arcane powers of denial.