Killer's Heart. If the Abysal Dragon kills a creature with Eldrich Missile, the Abysal Dragon heals Hp equal to any damage left over. For example, a barbarian has 16 Hp and takes 24 damage from the Eldrich Missile, the Abysal Dragon would heal 8 Hp.

Powerful Will. If the Abysal Dragon is subjected to an effect that would alter its personality or actions, or otherwise subject it to mental change against it's will, it automatically succeeds on the save.

Magic Resistance. The Abysal Dragon has advantage against all magic-related saving throws.

Multiattack. The Abysal Dragon can make either two gash attacks and a chomp attack, or it could replace the chomp attack with an Eldrich Missle or Menacing Glare.

Gash. Melee Weapon Attack: +18 to hit, reach 15 ft., 1 target. Hit:  29 (3d12 + 8) Slashing damage

Chomp. Melee Weapon Attack: +18 to hit, reach 10 ft., 1 target. Hit: 34 (3d20 + 8) Piercing  damage. If the target is a Large or smaller creature, the Abysal Dragon can choose to swallow the creature. If so, the creature must make a DC 25 Str saving throw or be swallowed by the dragon. While swallowed, the creature is Blinded and Deafened, and has total cover from all attacks outside of the dragon. The creature inside of the dragon can use its turn to make an attack against the dragon, which has vulnerability to Slashing damage from Magical or Elemental weapons from the inside. After the dragon takes 75 damage from this, it will then vomit the creature out. While inside the dragon, on each of the dragon's turns, the creature takes 6d10 acid damage, and cannot take reactions. The dragon can only have one creature swallowed at a time.

Eldrich Missle (4 turn cooldown). Ranged Magic Attack: +14 to hit, range 20/300 ft., 1 target. Hit: 60 (7d12 + 10) Necrotic damage.

Menacing Glare. The Abysal Dragon targets a creature. If the creature can see the Abysal Dragon, it must make a wisdom saving throw (DC 21). If the creature is immune to the frightened condition, it automatically succeeds the save. On a failed save, the creature has the frightened condition, centered on the Abysal Dragon. If the creature takes damage, or at the end of each of it's turns, it can repeat the saving throw. If the creature succeeds the save, or if the effect ends on it, that creature is immune to the dragon's Menacing Glare for the next 4 hours.

Move. The Abysal Dragon moves up to half of it's movement speed, assuming it is able to do so.

Evade. The next melee or ranged attack against the Abysal Dragon has disadvantage.