You create a two-foot-high black obelisk that guards a 10-foot radius area. Whenever a creature walks into the area or begins its turn within the radius it is hit with a blast of necrotic energy and must make a Constitution saving throw. On a failure the creature takes 1d10 necrotic damage and the creature’s speed is halved for 6 seconds, or half damage and no slowing effect on a successful save. The obelisk lasts for one day or until it has discharged energy 10 times.