The Bloodforge Arena

This small black Sphere measures 3/4 of an inch in diameter and weighs an ounce. Typically, 1d4 + 4 beads of force are found together. You can use an action to throw the bead up to 60 feet. The bead explodes on impact and is destroyed. Each creature within a 10-foot radius of where the bead landed must succeed on a DC 15 Dexterity saving throw or take 5d4 force damage. A Sphere of transparent force then encloses the area for 1 minute. Any creature that failed the save and is completely within the area is trapped inside this Sphere. Creatures that succeeded on the save, or are partially within the area, are pushed away from the center of the Sphere until they are no longer inside it. Only breathable air can pass through the sphere's wall. No Attack or other Effect can. An enclosed creature can use its action to push against the sphere's wall, moving the Sphere up to half the creature's walking speed. The Sphere can be picked up, and its magic causes it to weigh only 1 pound, regardless of the weight of creatures inside.