Valuk Rex

Lolth’s Chosen Monstrosity (Recharges after a Short or Long Rest). When the Valuk Rex is reduced to 0 hit points for the first time, it does not die. Instead, dark abyssal energy surges through its veins, its sail ignites with writhing shadow-flame, and it regains 440 hit points, It becomes wreathed in necrotic shadow, granting it resistance to all damage, Its attacks deal an additional 2d10 necrotic damage, and it regains any expended uses of Legendary Resistance. Additionally, the Valuk Rex now must use the options in the “Mythic Actions” section for 1 hour. It can not use the Legendary Actions during this time. Award a party an additional 155,000 XP (310,000 XP total) for defeating the Valuk Rex after its Lolth's Chosen Monstrosity activates.

Legendary Resistance (5/Day). If the Valuk Rex fails a saving throw, it can choose to succeed instead.

Abyssal Camouflage. When motionless, the Valuk Rex blends perfectly with stone and shadow. It gains advantage on Stealth checks to hide and cannot be detected by tremorsense or blindsight unless within 10 feet.

Terrifying Roar. Any creature that starts its turn within 120 feet and can hear it must make a DC 25 Wisdom saving throw or be frightened for 1 minute. Creatures can repeat the save at the end of each of their turns.

Magic Resistance. The Valuk Rex has advantage on saving throws against spells and other magical effects.

Spider’s Boon. Thanks to Lolth’s blessing, it can walk on walls and ceilings, leaving behind faint web traces.

Multiattack. Makes five attacks: one with its bite, two with its claws, one with its horns, and one with its tail.

Bite. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 62 (8d12 + 10) piercing damage. If the target is Huge or smaller, it is grappled (escape DC 27) and restrained.

Claw. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 38 (6d8 + 10) slashing damage.

Horn Gore. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 45 (6d10 + 10) piercing damage and the target must make a DC 27 Strength save or be knocked prone and stunned until the end of its next turn.

Tail Slam. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 48 (7d10 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 27 Strength save or be knocked back 30 feet.

Takes 5 legendary actions, choosing from the options below. Only one can be used at a time and only at the end of another creature’s turn.

• Detect. Makes a Wisdom (Perception) check.

• Move. Moves up to half its speed without provoking opportunity attacks.

• Tail Smash. Makes a tail attack.

• Horrific Roar (Costs 2 Actions). Each creature of its choice within 60 feet must succeed on a DC 25 Wisdom save or be frightened for 1 minute.

• Trample (Costs 3 Actions). Moves up to its speed through spaces occupied by Huge or smaller creatures. Each must succeed on a DC 27 Dexterity save or take 42 (12d6) bludgeoning damage and be knocked prone.

The Valuk Rex can take 3 mythic actions at the end of another creature’s turn, choosing from the options below. It regains spent mythic actions at the start of its turn.

Void Step. The Valuk Rex teleports up to 120 feet to an unoccupied space it can see, leaving behind a swirl of shadowy spider shapes that melt into the stone. Each creature within 10 feet of the space it left must succeed on a DC 25 Wisdom saving throw or be frightened until the end of their next turn.

Rending Shadows (Costs 2 Actions). Necrotic tendrils burst from its sail and tail, lashing creatures of its choice within 30 feet. Each must make a DC 25 Dexterity saving throw, taking 35 (10d6) necrotic damage on a failed save or half as much on a success.

Abyssal Bellow (Costs 3 Actions). The Valuk Rex unleashes a roar that distorts the very stone. Each creature of its choice within 90 feet must make a DC 25 Constitution saving throw. On a failure, the creature takes 55 (10d10) thunder damage, is deafened, and knocked prone. On a success, it takes half as much damage and isn’t knocked prone.