Vincent's prison arena

You create a 30 by 30-foot cube of translucent indestructible black walls in a spot within 30 feet of you. You can trap a maximum of 6 creatures and a minimum of 2 if there is more than 6 or less than 2 the spell fails. The creatures in the cube cannot escape with spells like dispel magic from the inside but a dispel magic or counterspell from the outside of the cube can end the spell. The spell ends when there is one creature left standing and all other creatures are unconscious or dead. Creatures on the outside of the cube can see in but creatures on the inside can not see out. There is dim light inside the cube.