Ioun Stone of Absorption

Requires attunement. A stone has AC 24, 10 hit points, and resistance to all damage.
Absorption: 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 dull gray, losing its magic.