Carcharoth, the Red Maw

Legendary Resistance (3/day). If Carcharoth fails a saving throw, he can choose to succeed instead.

Burning Silmaril. The Silmaril burns within Carcharoth's belly. While Carcharoth has more than half his hit points, the holy jewel only fuels his wrath. When Carcharoth is reduced to half his hit points or fewer, the Silmaril erupts with divine fire. At the start of each of Carcharoth's turns, he takes 10 (3d6) radiant damage. This damage ignores resistance, immunity, and cannot be prevented. 

While this trait is active:

• Carcharoth's Bite deals an additional 9 (2d8) radiant damage.
• Creatures that start their turn within 10 feet of Carcharoth take 5 (1d10) radiant damage.

Pain-Fueled Fury. Every wound only drives Carcharoth deeper into madness. For every 10 damage Carcharoth has taken since the start of his previous turn, he gains a +1 bonus to the damage rolls of all melee weapon attacks until the start of his next turn. At the start of his turn, after applying the bonus, the damage counter resets to 0. Maximum bonus: +12

Apex Predator. Carcharoth always knows the direction of any creature that has dealt damage to him within the last 24 hours, provided it is on the same plane.

Blood Frenzy. Whenever a creature within 60 feet drops to 0 hit points, Carcharoth may immediately move up to half his speed and make one Bite attack.

Siege Beast. Carcharoth deals double damage to objects and structures.

Multiattack. Carcharoth makes three attacks: one bite and two claw attacks.

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 31 (4d10 + 9) piercing damage + 13 (3d8) slashing damage. If Burning Silmaril is active, the Bite also deals: 9 (2d8) radiant damage. If the target is Large or smaller, it must succeed on a DC 22 Strength saving throw or become grappled (escape DC 22). Until this grapple ends, the target is restrained and Carcharoth cannot Bite another target.

Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 22 (3d8 + 9) slashing damage.

Rend.  If Carcharoth hits a creature grappled by his Bite with both Claw attacks on the same turn, the target takes an additional 36 (8d8) slashing damage and must succeed on a DC 22 Constitution saving throw or begin bleeding. A bleeding creature takes 10 (3d6) slashing damage at the start of each of its turns. The bleeding ends if the creature receives magical healing or another creature uses an action to stanch the wound.

Howl of Angband (Recharge 5-6).  Carcharoth unleashes a terrifying howl. Each enemy within 120 feet that can hear him must succeed on a DC 20 Wisdom saving throw or be frightened for 1 minute and have its speed reduced by 20 ft. The creature repeats the saving throw at the end of each of its turns, ending the effect on a success.

Bounding Leap. Carcharoth jumps up to 40 ft. to an unoccupied space he can see. This movement ignores difficult terrain and does not provoke opportunity attacks.

Savage Riposte. When a creature within 10 ft. misses Carcharoth with a melee attack, Carcharoth makes one Claw attack against that creature.

Carcharoth can take 3 Legendary Actions, choosing from the options below. Only one Legendary Action may be used at a time and only at the end of another creature's turn. He regains all spent Legendary Actions at the start of his turn.

Move. Carcharoth moves up to half his speed.

Claw. Carcharoth makes one Claw attack.

Crushing Bite (Costs 2 Actions). Carcharoth makes one Bite attack.