Uranium Dragon

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

Core Meltdown. If the dragon is reduced to 0 hit points, its body will start to destabilize over the course of 1 minute, eventually exploding in a catastrophic meltdown. All creatures within 90 feet of the dragon must make a DC 23 Dexterity saving throw, taking 110 (20d10) necrotic damage and being thrown back 15 feet, taking half as much on a successful one.

Radioactive Form. If a creature ends its turn within 10 feet of the dragon, they must succeed on a DC 23 Constitution saving throw or become poisoned until they succeed. After one success, the creature has advantage on the saving throw.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 20 (2d10 + 9) piercing damage.

Claw. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 16 (2d6 + 9) slashing damage.

Tail. Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 18 (2d8 + 9) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. 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 Frightful Presence for the next 24 hours.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

Nuclear Beam. The dragon exhales a concentrated beam of nuclear energy in a 120-foot line that is 10 feet wide. Each creature in that line must make a DC 23 Dexterity saving throw, taking 88 (16d10) necrotic damage on a failed save, or half as much damage on a successful one.

Nuclear Breath. The dragon exhales nuclear energy in a 30-foot cone. Each creature in that area must make a DC 23 Dexterity saving throw or take 44 (8d10) necrotic damage, or half as much damage on a successful 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 15 feet of the dragon must succeed on a DC 24 Dexterity saving throw or take 16 (2d6 + 9) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Critical Mass (Costs 3 Actions). The dragon releases a burst of atomic fire. All creatures within 30 feet of the dragon must make a DC 24 Dexterity saving throw, taking 55 (10d10) necrotic damage on a failure, or half as much on a success.