Bazelgeuse

Explosive Carapace. The bazelgeuse is covered in hundreds of bomb like scales, that detonate upon impact. Whenever the bazelgeuse takes physical damage all creatures within 5ft. of the creature must make a DC 18 dexterity saving throw or take 4 (1d6) fire damage and 4 (1d6) bludgeoning damage, halved on a success.

Concussive Blows. The bazelgeuse detonates its scales whenever it connects an attack adding a jarring explosion  to it's already powerful blows. Whenever a target is hit by a melee attack from the bazelgeuse it must make a DC 18 strength saving throw or be knocked back 5ft. If an obstacle would prevent this movement the targets takes 8 (2d6) bludgeoning damage and is knocked prone.

Legendary Resistances 3/day. When the bazelgeuse fails a saving throw, it may instead choose to succeed.

Multiattack. The bazelgeuse makes two Claw attacks and one Tail Slam.

Claw. Melee Natural Attack: +10 to hit, reach 10 ft., 1 target. Hit: 12 (2d6 + 4) slashing damage and 8 (2d6) bludgeoning damage and 8 (2d6) fire damage. 

Tail Slam. Melee Natural Attack: +10 to hit, reach 15 ft., 1 target. Hit: 28 (6d6 + 4) bludgeoning damage and 8 (2d6) fire damage. 

Carpet Bombing (Recharge 3-4). When the bazelgeuse flies it can shake free scales from its body which explode upon impact with the ground. A space up to 30ft. long and 15ft. across below the flight path of the bazelgeuse is effected by this attack, creatures within the area must make a DC 18 dexterity saving throw or take 24 (6d6) bludgeoning damage and (6d6) fire damage, halved on a success.

Blasting Breath (Recharge 5-6). The bazelgeuse lets out a crackling cloud of a gunpowder like substance in a 60ft. cone that results in a massive detonation. Creatures in the area must make a DC 18 dexterity saving throw or take 36 (9d6) bludgeoning damage and 36 (9d6) fire damage, halved on success. On a fail the creature also gets coated in the substance, and the next attack against them adds 8 (2d6) bludgeoning and 8 (2d6) fire damage to itself as it detonates the remaining mixture.

Last Resort. The bazelgeuse can heal from even the most grievous wounds, and will not stay for a fight it cannot win. When the bazelgeuse is brought to below half its health, it can use its reaction to shed its tail into an adjacent 5ft. square, resulting in the loss of its Tail Swing attack. The tail is detonated by Light the fuse, resulting in a cacophonous explosion. All creatures within 30ft. must make a DC 18 dexterity saving throw or take 40 (10d6) fire damage and 40 (10d6) bludgeoning damage, halved on a success.

The bazelgeuse has 3 legendary actions, which it can use after the end of another creatures turn. These actions restore at the beginning of its turn.

Move (Costs 1 Action). The bazelgeuse can move up to its movement speed.

Shed (Costs 1 Action). The bazelgeuse sheds five scales into five squares within 30ft. When detonated by Light the fuse the scales explode, dealing 8 (2d6) bludgeoning and 8 (2d6) fire damage to creatures in adjacent squares.

Light the fuse (Costs 1 Action). The bazelgeuse releases a high pitch trill, detonating any scales on the battlefield or its detached tail.