Tamminy's Ring of Equivalence

A ring of distortion warps the area around you.

Designate any number of creatures in a 30 foot radius, their movement speed is halved, and they must succeed on a Wisdom check against your spell save DC or lose all advantages and magical bonuses for one round. A creature may repeat this saving throw at the end of their turn. On a success, they are immune to the effects until they enter the area again, or until they end their next turn within it. 

Only ring a gal could ask for.