Actions

Multiattack. You can make 5 attacks. 1 with your bite, 3 claw, and 1 with your tail. Or fire 5 Malicebolts.

Frightening Presence. At the beginning of combat, when you first transform, each creature that is aware of you must make a DC 21 wisdom saving throw or become frightened of you. A creature frightened this way must spend its entire turn running as far away from you as possible, and it can't willingly approach you. At the end of its last action phase (the action phase when it as used all its actions) the creature can repeat the saving throw, ending this effect on a save. Once a creature saves, it cannot be frightened in this way for 24 hours.

Bite. Hit: +14, damage 2d6+7 piercing damage, 2d6 necrotic damage. On a hit, they must make a DC 21 constitution saving throw or gain one level of taint

Claw. Hit: +14, damage 2d6+7 slashing damage, 2d6 necrotic damage. On a hit, they must make a DC 21 constitution saving throw or gain one level of taint

Tail Slam. Hit: +14, damage 2d8+7 bludgeoning damage.

Malicebolt. Hit+13, damage 2d8+6 necrotic damage.

Black Lightning Discharge (recharge 4-6). As an action, you can discharge black lightning in a 25ft radius sphere centered on you. Each creature affected must make a DC 21 Dexterity saving throw or take 5d6 lightning damage + 5d6 necrotic damage. On a success they take half damage. On a hit, they must make a DC 21 constitution saving throw or gain one level of taint.

Koku Oohamaru(Recharge 5-6). You fire a large dark Maho Hamaru up 80ft from you. Each creature within 30ft of that point must make a DC 21 Dexterity saving throw or take 12d8 necrotic damage. On a success they take half damage. Additionally, any creature hit must make a DC 21 Constitution saving throw or gain one level of taint.

Black Lightning Bolt(recharge 5-6). As an action you can exhale a breath of black lightning in a line up to 80ft. Each creature affected must make a DC 21 Dexterity saving throw or take 5d6 lightning damage + 5d6 necrotic damage. On a success they take half damage. On a hit, they must make a DC 21 constitution saving throw or gain one level of taint.

Villain Actions

Round 1: Predatory Pounce. You leap toward any creature within your movement speed. When you land, the creature must make a DC 19 dexterity saving throw or take 4d8 bludgeoning damage is knocked prone. On a save they take no damage and isn't knocked prone.

Round 2: Malicious Energy. You gather release dark energy, increasing your power as it coats you in a dark lightning aura for 1 minute. For the duration of this ability, all your attacks deal an extra 1d6 lightning damage, and your Black Lightning Vengeance ability deals an extra d8 lightning damage. As you finish charging, red lightning explodes in a 10-foot radius around you. Each creature in the area must make a DC 21 Strength saving throw, taking 38 (13d6) lightning damage, and be pushed back 15 feet on a failed saving throw or half as much damage and isn't knocked prone on a successful one.

Round 3: Kokuraiju's Wrath. You let out a roar that shakes the heavens, letting all those who hear it know your rage. When you unleash this roar, your Frightening Presence action triggers forcing everyone to make the save again. If they gained immunity from being frightened by you from that ability, they still have to make the saving throw or be frightened again. As you finish a roar a colossal bolt of red lightning crashes on to the ground. Every creature in combat must make a DC 21 Dexterity saving throw or take half their maximum hit points dark lightning damage (minimum 1) on a fail, and half as much on a save. Additionally, they must make a DC 21 Constitution saving throw or become blinded, deafened, and stunned for 1 round.
Additionally, for the next three rounds of combat, you gain resistance to all types of damage and immunity to all types of conditions, as your seething anger pushes you past your limits.

Reactions

You can take three reactions in one round.

Vengeful Retaliation. If a creature within melee range misses you, you can make one tail attack at it.

Spiteful Pursuit. If a creature moves away from you, you can use your reaction to move up to half your speed to follow it.

Malice Bolt. After a creatures turn you can make one attack with your Malice Bolt

Lair Actions

Choose 1 lair action each round, or roll a 1d4, the same lair action cannot be used twice in a row.
Fires of Yomi. Pillars of hellfire erupt below every living creature within your lair. Each creature in the area must make DC 21 Dexterity saving throw, or takes 4d6 dark fire damage.

Lightning of the Kokuraiju. Bolts of red lightning strikes every living creature within your lair. Each creature must make a DC 21 Dexterity saving throw, or takes 4d6 dark lightning damage.

Dark Wave. Negative waves of energy are exuded from your body, affecting each creature in your lair. Each creature must make a DC 21 Constitution saving throw, or lose half their current hit points (minimum 1)

Taint Surge. A sudden shockwave of taint is unleased from your body. Every creature in your lair must make a DC 21 Constitution save, or gains one level of taint. If they are wearing a jade necklace they automatically save, but the jade necklace shatters.

The immediate area turns dark as the sky turns red and the clouds turn black. A 500ft radius sphere of taint materializes and each creature within that area must make a DC 21 constitution saving throw at the start of each round.