Armageddon

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

Magic Resistance. The Armageddon has advantage on saving throws against spells and other magical effects.

Reflective Carapace. Any time the Armageddon is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d6. On a 1 to 5, the Armageddon is unaffected. On a 6, the Armageddon is unaffected, and the effect is reflected back at the caster as though it originated from the Armageddon, turning the caster into the target.

Siege Monster. The Armageddon deals double damage to objects and structures.

Amphibious. The Armageddon can breathe air and water.

Multiattack.  The Armageddon can use its Frightful Presence. It then makes five attacks: one with its bite, two with its claws, one with its horns, and one with its tail. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 36 (4d12 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the Armageddon can’t bite another target.

Claw. Melee Weapon Attack: +19 to hit, reach 15ft., one target. Hit: 28 (4d8 + 10) slashing damage.

Horns. Melee Weapon Attack: +19 to hit, reach 10ft., one target. Hit: 32 (4d10 + 10) piercing damage.

Tail. Melee Weapon Attack: +19 to hit, reach 20ft., one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Frightful Presence. Each creature of the Armageddon’s choice within 120 feet of it and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if the Armageddon is within line of sight, 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 Armageddon’s Frightful Presence for the next 24 hours.

Swallow. Armageddon makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite’s damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the Armageddon, and it takes 56 (16d6) acid damage at the start of each of the Armageddon’s turns.

If the Armageddon takes 60 damage or more on a single turn from a creature inside it, the Armageddon must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the Armageddon. If the Armageddon dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

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

Fire Breath. The Armageddon exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 71 (13d10) fire damage on a failed save, or half as much damage on a successful one.

Weakening Breath. The Armageddon exhales gas in a 90-foot cone. Each creature in that area must succeed on a DC 24 Strength saving throw or have disadvantage on Strength-based attack rolls, Strength checks, and Strength saving throws 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.

Sleep Breath. The Armageddon exhales sleep gas in a 90-foot cone. Each creature in that area must succeed on a DC 21 Constitution saving throw or fall unconscious for 10 minutes. This effect ends for a creature if the creature takes damage or someone uses an action to wake it.

Lightning Breath. The Armageddon exhales lightning 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) lightning damage on a failed save, or half as much damage on a successful one.

Repulsion Breath. The Armageddon exhales repulsion energy in a 30-foot cone. Each creature in that area must succeed on a DC 23 Strength saving throw. On a failed save, the creature is pushed 60 feet away from the Armageddon.

Acid Breath. The Armageddon exhales acid in an 90-foot line that is 10 feet wide. Each creature in that line must make a DC 22 Dexterity saving throw, taking 63 (14d8) acid damage on a failed save, or half as much damage on a successful one.

Slowing Breath. The Armageddon exhales gas in a 90-foot cone. Each creature in that area must succeed on a DC 22 Constitution saving throw. On a failed save, the creature can't use reactions, its speed is halved, and it can't make more than one attack on its turn. In addition, the creature can use either an action or a bonus action on its turn, but not both. These effects last for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself with a successful save.

Cold Breath. The Armageddon exhales an icy blast in a 90-foot cone. Each creature in that area must make a DC 24 Constitution saving throw, taking 67 (15d8) cold damage on a failed save, or half as much damage on a successful one.

Paralyzing Breath. The Armageddon exhales paralyzing gas in a 90-foot cone. Each creature in that area must succeed on a DC 24 Constitution saving throw or be paralyzed 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.

Poison Breath. The Armageddon exhales poisonous gas in a 90-­-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 77 (22d6) poison damage on a failed save, or half as much damage on a successful one.

Change Shape. The Armageddon magically polymorphs into a humanoid or beast that has a challenge rating no higher than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (the Armageddons choice).

In a new form, the Armageddon retains its alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, lair actions, and Intelligence, Wisdom, and Charisma scores, as well as this action. Its statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

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

Attack. The Armageddon makes one claw attack or tail attack.

Move. The Armageddon moves up to half its speed.

Chomp (Costs 2 Actions). The Armageddon makes one bite attack or uses its Swallow.

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

Wing Attack (Costs 2 Actions). The Armageddon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The Armageddon can then fly up to half its flying speed.