Blood Frenzy.Yuviir, Malar's Servant has advantage on melee attack rolls against any creature that doesn’t have all its hit points.

Death Throes. If Yuviir, Malar's servant is reduced to 0 hit points, its body erupts into sludge that fills a 10-foot-radius sphere. Each creature within that area must succeed on a DC 14 Dexterity saving throw or be covered in the sludge for 1 minute. While covered in the sludge, a creature’s speed is halved. A creature can use its action to scrape the sludge off itself or another creature within 5 feet of itself.

Multiattack. TheYuviir, Malar's Servant makes three Claw attacks. It can replace one claw attack with Petrifying Claws or a bite

Claw. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 5) slashing damage.

Petrifying Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) slashing damage, or 14 (2d10 + 3) slashing damage if the attack roll had advantage. If the target is a creature, it must succeed on a DC 12 Constitution saving throw, or it begins to turn to stone and is restrained until the end of its next turn, when it must repeat the saving throw. The effect ends if the second save is successful; otherwise the target is petrified for 24 hours.

Bite . Melee Weapon Attack: +9 to hit, reach 10ft., one target. Hit: 22 (3d8 + 9) piercing damage. If the target is a Large or smaller creature, it must succeed on a DC 15 Dexterity saving throw or be swallowed by the Yuviir. A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside Yuviir, and it takes 21 (6d6) acid damage at the start of each of Yuviir turns. If Yuviir takes 25 damage or more on a single turn from a creature inside it, Yuviir must succeed on a DC 21 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of Yuviir. If Yuviir dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 20 feet of movement, exiting prone.

Enlarge (Recharges after a Short or Long Rest). For 1 minute,Yuviir, Malar's magically increases in size, along with anything it is wearing or carrying. While enlarged, Yuviir is Large, doubles its damage dice on Strength-based weapon attacks (included in the attacks), and makes Strength checks and Strength saving throws with advantage. If the Yuviir lacks the room to become Large, it attains the maximum size possible in the space available. 

Violent Retaliation. If a creature within 10 feet of Yuviir, Malar's Servant hits it with an attack, the draconian can make one Claw attack against that creature. If the Claw attack hits, it deals an additional 4 (1d8) slashing damage.

Summoning Minions (Recharge 5-6)

Tell: At the end of Yuviir, Malar's Servant's turn, he opens his eyes, and a dreadful magical energy gathers like a pinprick of light deep inside of their pupil. When their gaze falls on a creature, it feels an impending sense of dread grow within itself.

Neutralization: The players must hide from Yuviir, Malar's Servant's turn so as to not be seen when the Battlefield Action reaches its Resolution phase. They can use the environment to block line of sight, take the Hide action, or even cast spells like Darkness to obscure the Yuviir,’ vision.

Resolution: If not neutralized, all creatures Yuviir can see have the Frightened condition. They can make a Wisdom saving throw to free themselves from this effect at the end of each of their turns with a DC of 16

*thanks Pointy Hat for this battlefield action fun !