Ouroboros

When the ouroboros is slain, it is reborn in a burst of energy in a 300-foot radius from its body. Roll any die. On an even result, the energy causes plants to grow, and creatures in the area regain 22 (5d8) hp. On an odd result, creatures in the area must make a DC 15 Constitution saving throw, taking 22 (5d8) necrotic damage on a failed save, or half as much damage on a successful one.

As a bonus action, the ouroboros gains immunity to one type of damage.

It can change this immunity from one type to another as a bonus action.

The ouroboros can use its Introspective Presence. It then makes two bite attacks.

Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) piercing damage.

Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 15 Wisdom saving throw or be incapacitated for 1 minute as the creature is overcome by introspective thoughts. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Introspective Presence for the next 24 hours.

The ouroboros exhales energy in a 30-foot cone. Each creature in that area must make a DC 15 Dexterity saving throw, taking 27 (6d8) damage on a failed save, or half as much damage on a successful one.

The damage is either acid, cold, fire, lightning, necrotic, poison, radiant, or thunder. The dragon chooses the type of damage before exhaling.

D5

When the dragon is hit with an attack, it gains resistance to damage of that type until the end of its next turn, including the damage from the attack that triggered this reaction.

The dragon can take 4 legendary actions, choosing from the options below. Only one legendary action 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.

4/TURN

The ouroboros 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 ouroboros regains spent legendary actions at the start of its turn.

The ouroboros makes one bite attack.

The ouroboros blurs and shifts light around itself or another creature it can see within 60 feet of it. Attacks against the target have disadvantage until the end of the ouroboros' next turn. The target can resist this effect with a successful DC 15 Wisdom saving throw.

The ouroboros causes itself or another creature it can see within 60 feet of it to illuminate with white flame. Attacks against the target have advantage until the end of the ouroboros' next turn. The target can resist this effect with a successful DC 15 Wisdom saving throw.