Twisted Fate. When an attack is made against Absolute Chaos they may roll 1d4. If Odds the attack will continue onward to hit them, if Evens the attack will instead be reversed back to the attacker for the same amount of damage.

Spellcasting. Absolute Chaos is a 9-level spellcaster. Its spellcasting ability is [Charisma] (spell save DC 18, +10 to hit with spell attacks). Absolute Chaos has following Wizard spells prepared:
Firebolt, Burning Hands 
Scorching Ray, Fireball 

Holy Weakness. Calling upon Cosmos in this time of Dire need will grant the party a casting of Holy, reducing Chaos' AC by 4, and lowering his HP by 200. 

Multiattack. Absolute Chaos can attack twice with his Flaming Greatsword, and once with either his Tail, his Claws, Fire Breath, or a Magic Attack (2 attacks per turn)

Flaming Great Sword. Melee Weapon Attack: +20 to hit, reach 10 ft., 1 target. Hit: 32 (4d10 + 10) [Slashing] damage. (additional 1d10 Fire Damage)

Claws. Melee Weapon Attack: +20 to hit, reach 10 ft., 1 target. Hit: 32 (4d10 + 10) [Slashing] damage.

Tail. Melee Weapon Attack: +20 to hit, reach 10 ft., 1 target. Hit: 40 (4d10 + 10) [Bludgeoning] damage.

Swallow. Melee Weapon Attack: +20 to hit, reach 10 ft., 1 target. DC 27 Strength save or else target is grappled and restrained. Target must make a DC27 strength check to attempt to force their way out of Absolute Chaos's stomach on the start of their turn, success will result in an ejection from Absolute Chaos, but the target will be knocked prone until helped or their next turn. 

Hellish Digestion. Melee Weapon Attack: Auto hit,, 1 target. Hit: 20  (2d10 + 10) [Fire/Acid] damage. (only usable if a target is swallowed)

Flames of Immolation. RangedWeapon Attack: +20 to hit, range 10/80 ft., 1-4 target. Hit: 70 (10d8 + 12) [Fire] damage. Ignores Fire Resistances and immunities

Chaotic Step: As a bonus action Absolute Chaos can warp to any point he can see or knows of.... anywhere

Retrebution. When attacked Absolute Chaos will point at the attacker and give the command word "BURN" dealing 1d20 fire damage to the target

As an Ancient Fiendish force Absolute Chaos is able to call upon the most dark of black magical rights to act as they see fit. 

Call Meteor (Costs 2 Actions). Chaos will begin raising his hands and chant unto the skies. "Per sánguinem Dómini invocábo mundum, * vastátio et perítio ad univérsam creaturam. Nunc age, et in te cadant Meteor"  (Players must deal 50 damage to him within 2 turns to stop this attack from landing. IF it does land, the attack will reduce all party members at full health to 1 hp, any party member below 100 HP will be killed (put into death saving throws)