Garroks’s spellcasting ability is Charisma (spell save DC 17). He can innately cast the following spells, requiring no material components.
Magic Resistance.Garrok has advantage on saving throws against spells and other magical effects. Devil's Sight. Magical darkness doesn't impede his darkvision.
Green Flame Blade Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) piercing damage. If the target is a creature other than a construct, it must succeed on a DC 17 Wisdom saving throw or lose 10 (3d6) hit points at the start of each of its turns due to an infernal wound. Each time Garrok hits the wounded target with this attack, the damage dealt by the wound increases by 10 (3d6). Any creature can take an action to stanch the wound with a successful DC 12 Wisdom (Medicine) check. The wound also closes if the target receives magical healing. Fireball (2/day) A bright streak flashes from your pointing finger to a point you choose within range and then blossoms with a low roar into an explosion of flame. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one. The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.
Hellish Rebuke. The Hellish Rebuke spell from Garrok's Innate Spellcasting is cast as a reaction.
Chains Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 10 (1d8 + 6) piercing damage. On a successful hit, the target must succeed a DC 12 Dexterity saving throw or be caught by the hook at the end of the chain, becoming Grappled. Garrok has 4 chains that can be used to attack. A chain that is currently grappling a creature cannot make an attack. If more than one creature is grappled by Garrok's chains, he has a -3 penalty to contested checks when creatures attempt to free break free of the chains.