Legion of the Abyss: 3 rounds into the fight, another Abyss Watcher enters the fray. It has 50 HP and 1/4th damage on attacks. 2 rounds after that, a third Abyss Watcher appears. It has red eyes and will attack the nearest thing to him, whatever that may be. Same stats as the weaker one. After one is killed, if it isn’t the boss itself, it will resurrect at full HP after 3 rounds.

They have access to the Stab, and dash slash abilities of the Boss

Multi-attack: Abyss watchers can attack three times with a stationary ability or two times with one movement ability and one stationary ability.

Stab: +11 to hit Abyss watcher stabs forward dealing Hit 14(3d4+7) piercing damage.

Dash slash: +11 to hit Boss leaps forward 15 feet dealing 21(3d8+7) damage to all enemies in a 5 ft radius in a line. 3x5 blocks or 15x25 feet.

Uppercut: +11 to hit  Swings sword up, throws dust causing Disadvantage on next attack. Con saving throw of DC 14. On a fail, target gets knocked prone.

Jump Slam: +11 to hit Boss Jumps up to 30 feet toward a character and slams weapon down dealing 21(4d6+7) damage in a 3x3 area around the boss.

When boss dies, it resurrects to full health. It’s sword and dagger are now on fire, and no additional enemies spawn and the remaining living ones die. He no longer has access to jump slam or Dash slash and gains fire resistance.

Dash Burn: +11 to hit The boss dashes forward 30 feet (fixed distance). He must pass an AC check for anyone in the 1x3 block area on the BOSSES LEFT side for 25 (5d8+7). Then, regardless of being hit, those players must make a DC 16 check or get hit for 14 (4d6) fire damage.

All of the previous attacks now deal 10 (3d6) fire damage DC16.