Rolling Icosahedron

At the top of a dais sits a 5-foot-tall, 20-sided stone. Each triangular facet is tiled with a mosaic depicting a crowned humanoid.

If a creature approaches within 30 feet of the stone without swearing allegiance to the ancient empire that crafted it, the stone begins to magically roll of its own accord. Roll initiative. Each round on initiative count 15, the stone takes an action based on the nature of the portrait that is currently uppermost on the stone—smiling, frowning, or shouting. On the stone’s first turn, a frowning mosaic portrait is currently uppermost. At the end of each of its turns, roll a d20 to determine what action the stone takes on its next turn.

The stone magically senses the locations of living creatures within 60 feet. The stone moves in straight lines and can move up slopes as steep as 45 degrees. If a creature or object stands between the stone and its destination, the stone collides with the obstacle, dealing 49 (14d6) bludgeoning damage. If this damage reduces the obstacle to 0 hit points, the stone continues its movement. Otherwise, its movement ends for the turn. A creature can make a Strength saving throw to halt the stone’s progress without taking damage.

1–5 Shouting Face: The stone moves 60 feet in the direction of the closest creature within 60 feet. When the stone stops moving, it emits a burst of flame. Each creature within 30 feet makes a Dexterity saving throw , taking 52 (15d6) fire damage on a failed save or half damage on a success.

6–15 Frowning Face: The stone moves 60 feet in the direction of the closest creature within 60 feet. Each time the stone moves within 5 feet of a creature, that creature must make a Constitution saving throw , taking 10 (3d6) necrotic damage on a failure or half damage on a success.

16–20 Smiling Face: The stone moves 30 feet in the direction of the closest creature within 30 feet. The first time the stone moves within 5 feet of a creature, it stops moving and emits a blue glow that magically restores 10 (3d6) hit points to that creature. The stone doesn’t move again until the next round.

If there are no creatures within 60 feet of the stone at the start of its turn, it moves 60 feet towards its original position. Once at its original location, the trap resets.

Icosahedron. The stone is an icosahedron—a shape with 20 sides. A creature that makes a History check knows that the portraits represent twenty emperors from a long-past empire. On a critical success, the creature remembers that the stone was used to secure palaces against traitors. The stone is an object with AC 19, 400 hit points, immunity to poison and psychic damage, and vulnerability to bludgeoning, force, and thunder damage.

Magical Effect. This is a magical effect created by evocation and transmutation magic. Casting dispel magic on the icosahedron requires a spellcasting ability check and disables the face that’s currently uppermost, dispelling that effect only. For instance, while a shouting portrait is uppermost, dispel magic causes any future rolls of 1–5 to have no effect. If the shouting and frowning effects are dispelled, the stone stops moving and the trap is disabled.