Arcane Prism

You summon a glowing prism of pure arcane energy. It floats there and bursts, teleporting creatures around, shooting beams of force, and causing general mayhem. The prism hovers 5 feet of the ground and is impervious to all damage. It is about 3 feet tall and 2 feet in diameter, and it is made of a sparkling, crystalline material. It’s actions each round depend on how long it’s been active. It acts on initiative count 20, and moves 10 feet towards the nearest enemy before it makes an action.

Round 1: The prism fires a beam of energy at the nearest hostile creature. Make an attack roll with +8 to hit, on a success, the target takes 5d10 force damage.

Round 2: The prism targets two enemy creatures within 30 feet of it, and swaps their locations (they teleport to the other target’s spot).

Round 3: The prism targets an enemy creature within 30 feet. That creature must make a DC 17 Wisdom saving throw or move up to its speed and attack the nearest creature that is hostile to you.

Round 4: The prism casts Polymorph on an enemy creature within 30 feet. On a success, it turns them into a frog.

Round 5: The prism summons a wall of crystal 10 feet tall and 30 feet wide in an unoccupied space within 30 feet of your choice. It has 100 hit points and an AC of 10, and it lasts until the prism’s next turn.

Round 6: The prism creates an illusions of you equal to your spellcasting modifier. These duplicates move with you and function like the Mirror Image spell, except when one duplicate disappears, roll 1d4. The result is how many extra duplicates take its place. These duplicates last until the prism’s next turn.

Round 7: The prism raises each corpse within 30 feet as a wight with the equipment of the original creature. The wights follow your commands, act on the prism’s turn, and last for 1 minute, when they become lifeless corpses again.

Round 8: The prism reveals a glimpse into the future. You and each ally that can see the prism gain advantage on all ability checks, attack rolls and saving throws until the prism’s inevitable detonation.

Round 9: Detonation.

At any time between round 1 and round 9, you may detonate the prism. It automatically detonates once it reaches round 9. Once the crystal detonates, each creature with 30 feet of the crystal must succeed on a successful DC 18 Dexterity saving throw or take 12d12 force damage, or half as much on a successful save. Also, each damaged creature is pushed back 30 feet and knocked prone. On a successful saving throw, the creature is not knocked prone.