Euhedral

Prismatic Antimagic Reflection. The Euhedral has advantage on saving throws against spells, and any creature making a spell attack against the Euhedral has disadvantage on the attack roll. If the Euhedral succeeds on its saving throw against a spell or a spell attack misses it, an additional effect might occur, as determined by rolling a d6:

1–2. If the spell affects an area or has multiple targets, it fails and has no effect. If the spell targets only the Euhedral, it has no effect on the Euhedral and is reflected back at the caster, using the spell slot level, spell save DC, attack bonus, and spellcasting ability of the caster.

3–4. No additional effect.

5–6. The Euhedral's crystals converts some of the spell’s energy into a burst of destructive force. Each creature within 30 feet of the Euhedral must make a DC 16 Constitution saving throw, taking 4 (1d8) force damage per level of the spell on a failed save, or half as much damage on a successful one.

Piezoelectric Discharge. Whenever a creature within 5 feet of the Euhedral hits it with a Melee attack, the attacker takes 4 (1d8) lightning damage and must make a DC 16 Constitution saving throw. On a failed save, the target loses its Reaction and its Speed is halved until the end of its next turn.

Multiattack. The Euhedral makes two Resonance Strike attacks or two Prismatic Shard attacks, and Harmonic Blast (if available).

Resonance Strike. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 9 (1d10 + 3) slashing damage plus 4 (1d8) lightning damage.

Prismatic Shard. Ranged Weapon Attack: +6 to hit, range 60/120 ft., one target. Hit: 9 (1d10 + 3) piercing damage plus 4 (1d8) lightning damage.

Harmonic Blast  (Recharge 5–6). The Euhedral emits a high-frequency, resonant sonic wave in a 30-foot Cone. Each creature in that area must make a DC 16 Constitution saving throw. On a failed save, a creature takes 27 (6d8) thunder damage and is pushed 10 feet away. On a successful save, a creature takes half as much damage and isn't pushed. Nonmagical crystalline structures, glass, and stone objects in the area automatically take maximum damage.

Prismatic Refraction. The Euhedral refracts ambient light across its faceted body. Each creature of the Euhedral's choice within 20 feet that can see it must succeed on a DC 16 Constitution saving throw or gain the Blinded condition until the start of the Euhedral's next turn. A target can avert its eyes to automatically succeed on the save, but attacks against the Euhedral before the start of the target's next turn are made with Disadvantage.