Thardraxxus

Thardraxxus was a black dragon of determinant age who lived in the Rootgarden Marsh in Tal'Dorei, where it was friends with a manawort and protected it and a group of sporelings.

Thardraxxus was first mentioned in Critical Role: Tal'Dorei Campaign Setting. So far, they have neither appeared nor been mentioned onstream.

Black dragon abilities

 * Natural armor — Thardraxxus possessed natural armor, granting them an armor class between 17 and 22.
 * Speed — Thardraxxus could move between thirty and forty feet, fly between sixty and eighty feet, or swim between thirty and forty feet per round.
 * Immunities — Thardraxxus was immune to acid damage.
 * Senses — Thardraxxus possessed blindsight of up to between ten and sixty feet and darkvision of up to 120 feet.
 * Amphibious — Thardraxxus could breathe in air and water.
 * Legendary Resistance — If old enough, Thardraxxus could, thrice a day, choose to succeed a failed saving throw.
 * Actions:
 * Bite — A melee weapon attack that, on a hit, dealt piercing and acid damage.
 * Claw — A melee weapon attack that, on a hit, dealt slashing damage; this attack was not usable as a wyrmling.
 * Tail — A melee weapon attack that, on a hit, dealt bludgeoning damage; this attack was not usable as a wyrmling.
 * Frightful Presence — If older than a wyrmling, Thardraxxus could force creatures of their choice within 120 feet to potentially become frightened of them for up to a minute; creatures who fail to succumb to the effect become immune to it for twenty-four hours.
 * Acid Breath — Thardraxxus could exhale a line of acid between five and ten feet wide and fifteen and ninety feet long, spraying creatures who failed to dodge it with a variably large amount of acid damage, depending on the dragon's age.
 * Legendary Actions — If Thardraxxus was young or ancient, they would have the following abilities:
 * Detect — Thardraxxus could make a Perception check.
 * Tail Attack — Thardraxxus could attack with their tail.
 * Wing Attack — Using two actions, Thardraxxus could beats their wings, forcing creatures within ten feet to try to dodge the attack or take bludgeoning damage and get knocked prone, after which the dragon could fly up to half their flying speed distance.

Trivia

 * Thardraxxus's age was determinant, depending on the requirements of whatever campaign they were used in.