Asura is clearly scarred angered beast, it resembles a once human, something that represents Fauruns anger in fire form

Multiattack. The giant makes two attacks, using Flame Sword or Hammer Throw in any combination.

Flame Sword. Melee Attack Roll: +11, reach 10 ft. Hit: 21 (4d6 + 7) Slashing damage plus 10 (3d6) Fire damage.

Hammer Throw. Ranged Attack Roll: +11, range 60/240 ft. Hit: 23 (3d10 + 7) Bludgeoning damage plus 4 (1d8) Fire damage, and the target is pushed up to 15 feet straight away from the giant and has Disadvantage on the next attack roll it makes before the end of its next turn.

Flurry Combos. The user of Asura grows an additional 4 arms, each arm requires the creature its attacking a Dexterity Saving Throw (DC 14), if it hits, each arm deals 5 (1d6+ 2 fire damage) 

Additionally, at 3rd level your destructive techniques can even weaken your enemies defenses.

While you're raging, immediately after you hit a creature with an unarmed strike, you can take a bonus action to attempt to break their defenses. Make a Strength check with a DC equal to the target's AC. On a success, the target's AC is reduced by half of your proficiency bonus (rounded down) until it finishes a short or long rest. Its AC cannot be reduced in this way more than once.

However, for every summon of the Asura, the user takes 4 hit points of fire damage and when deactivated user receives an additional 3d6 psychic damage

Legendary Swipe. When a creature within 10 feet of the Asura targets the user with a physical attack, the Asura can use its reaction to swipe at the enemy. The attacker must make a Dexterity Check DC 17 to avoid the swipe. If Dexterity check fails attack lands on user, if Dexterity Check fails the attacker is swiped away 5 feet and take 1d4 bludgeoning damage.

If you want standard mechanical vulnerabilities, tie them to traditional Vedic or Buddhist lore regarding Asuras.

Asuras are often cosmic beings of fire and wrath. If your boss relies more on divine magic, illusion, or reality-warping presence, try these thematic options:

• Gaze of the Six Faces (Costs 1 Action): The Asura turns one of its faces toward a creature it can see within 60 feet. The target must succeed on a DC [12] Wisdom saving throw or become frightened until the end of its next turn.

• Asuric Roar (Costs 2 Actions): The Asura lets out a reality-shaking war cry. Each creature within 30 feet must make a DC [14] Constitution saving throw. On a failure, a creature takes 4d6 thunder damage and is knocked prone. On a success, they take half damage and aren't knocked prone.

• Ignite Pride (Costs 3 Actions): The Asura targets a creature it can see within 90 feet, telepathically twisting their own ego. The target must make a DC [16] Charisma saving throw. On a failure, the target must immediately use its reaction to make a melee weapon attack against its closest ally.