The Ogre Duke’s innate spellcasting ability is Charisma (spell save DC 13). Ogre King can innately cast the following spells, requiring no material components:
Magic Resistance. The duke has advantage on all saving throws against magic or spell-like effects.
Multiattack. The Ogre Duke makes two trident attacks. Trident. Melee Weapon Attack, +7 to hit, 5 ft. One target, 8 (1d8+4) piercing damage and the target must make a grapple check against the Ogre. On a failure, they are dragged into the ring of crystals on the ogre's stomach and they take 2d6 piercing damage. The Duke heals half that amount. Energy Pulse (recharge 4,5,6). A wave of arcane energy in a line 30 ft by 5 feet shoots out of the crystals on the dukes chest. All creatures within that line must make a dexterity saving throw DC 14. On a failure they take 5d8 force damage and are knocked prone. On a success, they take half damage and are not knocked prone.
Hexed Aura (recharge 6). The Duke summons an aura in a circle 60 ft surrounding him. Any creature that starts its turn in the circle must make a Constitution Saving throw DC 16. On a success there is no effect. On a failure the creature can only take one action, or one bonus action, or one movement action. The aura lasts until the beginning of the duke's next turn.