Keen Perception. The Trilendego has advantage on wisdom (Perception) checks involving smell or moving creatures made of flesh.

Regeneration. The Trilendego’s incredible constitution gives it an extraordinary ability to automatically heal wounds as they happen. At the start of each of the [monster name]’s turn, roll 3d8 + 6 and add the total to the [monster name]’s hit points.

Multiattack. The Trilendego can make 3 attacks. 2 with its claws and one bite attack.

Rage. Once per day, the Trilendego can enter a rage. (See PHB pg. 42)

Frightful Presence. Any creature within 30 ft. of this creature that can see it must make a WIS saving throw, DC 20 or be frightened of Trilendego for 1 minute. Any creature frightened by Trilendego can make another WIS saving throw at the start of its turn, on a success, they are no longer frightened.

Screech. While not in direct sunlight, the Trilendego can 1/day let out a powerful screech that shakes any living creature to their core.

Spellcasting. The Trilendego is a 2nd-level spellcaster. It can use the following spells at their respective levels:

2nd-level: Invisibility (At Will)

2nd-level: Enlarge 1/day

Bite. Melee Weapon Attack: +11 to hit, reach 5ft., 1 target. Hit: 15 (4d6 + 6) piercing damage.

Claw. Melee Weapon Attack: +13 to hit, reach 5 ft./10 ft., 1 target. Hit: 27 (6d8 + 7) slashing damage. 

Screech. Each creature within 60 ft. of the Trilendego that can hear it must make a CON saving throw DC 20 or take 24 (6d8) necrotic damage.

Some legendary actions are only available to the Trilendego when in within its lair.

Increased Dash (Costs 1 Actions). When using this legendary action, the movement speed of Trilendego is tripled.

Stomach Acid (Costs 2 Actions). The Trilendego stabs it’s own stomach, dealing damage as normal, to coat its claws in stomach acid, giving the creature an extra 1d12 acid damage per hit with its claw attacks, for next 2 turns.