Birunallian Worm

Glorious Scales:
Immunity to any melee attack made by a person under the base strength of 20

Immunity to Fire:
The creature is fully immune to fire damage no matter what.

Weakness to Poison:
The creature takes double damage from poison and players have an advantage on saving throws against it if it is engulfed in poison.

Weakness to Necromancy and Psychic Damage:
The creature takes double damage from Necrotic and Psychic damage.

Multi-attack:
This creature can attack twice, once with bite and once with rampage.

Bite:
The creature sinks its teeth into another creature +10 to hit, target 1 creature. On hit deal 4d10 piercing damage.

Rampage:
The creature attacks violently in a 20 feet radius, +8 to hit, target multiple creatures within range. On hit deal 8d4 bludgeoning damage.

Swallow:
The beast would dive into the ground, as it came out of the ground underneath a player head first, it swallowing them whole, delivering 3d10 of damage if the player fails a Dexterity Saving Throw.

Titanic Squash:
The beast would raise it's tail upwards as it slammed down on the player dealing 3d8 of damage if the player fails a Dexterity Saving Throw, as well as Dazing it's opponent and making them Prone.

Acidic Mayhem:
The beast would rise 20 Feet into the air, as it spits a cone of acid 30 feet in front of it, anyone in the range has to roll a Dexterity Saving Throw to dodge, or they will take 2d10 worth of damage for 2 rounds.