Weakened Wyrm Queen

Semi-Aquatic. The wyrmqueen can hold her breath for 8 hours.
Mostly Immortal. As long as she dies in her pool she will come back to life in 1d8 days
Bloated Stomach. When the Wyrm queen dies she floats to the surface and sits there for 1d8 hour

Attacks. The Wyrmqueen makes one attack action every turn.

Action melee weapon Attack. Bite Attack: +6 to hit, reach 20 ft., 1 target. Hit: 10 (1d12 + 3) piercing damage and 1d6 poison damage

Action melee Attack. Ranged Tailwhip Attack: +6 to hit, range 25 ft., 1 target. Hit: 9 (2d6 + 3) bludgeoning damage. The target must make a DC 14 strength saving throw or be pushed back 15 feet away from the Wyrmqueen.

Enter the description for how bonus actions work for your monster here.

Canceling Cascade. If a creature casts a spell with a verbal component within 60 feet of it, the Wyrmqueen can Splash water while within 30 feet of the spellcaster to rise up and splash against the spellcaster. The spellcaster must succeed on a DC 14 Constitution saving throw or it fails to cast the spell, losing its action for the turn but not its a spell slot.