Amphibious. The dragon can breathe air and water.

War Carriage. The dragon carries a custom-made carriage that allows four Medium creatures or one Large creature to be transported on its the back, or a total of 2,000 pounds, not counting the weaponry. This carriage is attached to the creature by four leather straps and harnesses which, if severed, cause it to tumble off the creature’s back. Each of the straps of this war carriage are Tiny objects with AC 18 and 15 hp and immunity to poison and psychic damage, and resistance to bludgeoning and acid damage.

Mounted Weaponry. The dragon's carriage holds a massive ballista strapped tight to its body. Any humanoid creature within the carriage can make an attack with this weapon as an action (see the dragon's Actions).

Multiattack. The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage plus 4 (1d8) acid damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Acid Breath (Recharge 5–6). The dragon exhales acid in a 30­-foot line that is 5 feet wide. Each creature in that line must make a DC 14 Dexterity saving throw, taking 49 (11d8) acid damage on a failed save, or half as much damage on a successful one.

Ballista (Rider Only). Ranged Weapon Attack: +6 to hit, range 120/480 ft., one target. Hit: 16 (3d10) piercing damage.

As a reaction, the Young Black War Dragon can attack with a gore or stomp attack, but only if it´s attaced by a melee attack. Gore deals 10D6 piercing damage on a unsuccesful Strength 15 check, and half as much on a succesful one. Stomp deals 11D8 bludgeding damage of an unsuccessful Strength 18 check and half as much on a succesful one.

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.