Chaotic Ancient Black Dragon

Acidic The dragon can you acid on the ground within a 5 ft radius in front of creature. Acid causes 5 hit points of damage till dealt with with with a med kit. 

Legendary Resistance (3/Day, or 5/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.

Multiattack. The dragon makes two Rend attacks and a claw attack. It can replace one attack with a use of Spellcasting to cast Melf’s Acid Arrow (level 4 version).

Rend. Melee Attack Roll: +15, reach 15 ft. Hit: 17 (2d8 + 8) Slashing damage plus 9 (2d8) Acid damage.

Acid Breath (Recharge 5–6). Dexterity Saving Throw: DC 22, each creature in a 90-foot-long, 10-foot-wide Line. Failure: 67 (15d8) Acid damage. Success: Half damage.

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 21, +13 to hit with spell attacks):

At Will: Detect Magic, Fear, Melf’s Acid Arrow (level 4 version)

Blood Rage The devil deals an additional 10 damage with melee weapon attacks after being attacked 

Resistance The dragon has electricity, acid, slashing, and poison resistance

Weapons In Hand Melee Attack + 8 to hit, 10 feet reach, one target. Hit: 40 (4d10 + 6) bludgeoning damage plus (2d6) bludgeoning damage if the creature doesnt have full health 

Bit melee attack + 6 to hit, reach 5 ft, one target limit, Hit 15 (2d6+5) piercing damage DC 15 constitution saving throw, taking 21 damage (6d6) poison damage on failed saving throw or half on saving throw success 

Claw melee attack +6 to hit, reach 5 ft, one target. Hit 25 (2d8+5) slashing damage and the target must succeed DC 15 constitution saving throw or be paralyzed for 1 minute. They can repeat the roll after each round to end the effects. 

Multiattack Upon successful bit attack creature momentarily bits down for an additional claw attack

Retreat if hit points are 20 or more creature can flap its wings to fly back 10 ft 

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature's turn , the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each its turns.

Spiked Tail Attack Hit 12 (2d8+5)  bludgeoning and piercing damage

Spit Stone range attack +11 to hit range 60/150 ft, one target Hit: 17 (2d10+5) bludgeoning damage 

Wing Attack the dragon beats its wings, all creatures within 10 ft roll for DC on saving throw 19 Dexterity or take 13 (2d6 + 6) pludgeoning damage and knocked prone. The dragon can fly up half its flying speed.

Frightful Presence. The dragon uses Spellcasting to cast Fear. The dragon can’t take this action again until the start of its next turn.The dragon wars and every creature within 100 ft rolls a constitution saving throw DC 19 upon failure is stunned for one round. 

Pounce. The dragon moves up to half its Speed, and it makes one Rend attack.