Bodily Features. Zargon's horn "regrows" Zargon after 1d4 days. The horn is destroyed if it is dropped into the Eye of Zargon, far below in the lost city, within one day of Zargon's death.

Additionally, Zargon has 18 tentacles: 6 barbed tentacles attached to each of his shoulders, and 6 muscled tentacles stemming from the base of his trunk. Each tentacle can grapple one target.

Amphibious. Zargon can breathe air and water.

Anathematic Secrecy. Zargon can't be targeted by any divination magic or perceived through magical scrying sensors.

Charge. If Zargon moves at least 10 feet straight toward a target and then hits it with a gore attack on the same turn, the target takes an extra 26 (4d12) piercing damage. If the target is a creature, it must succeed on a DC 27 Strength saving throw or be pushed up to 10 feet away and knocked prone.

Corrosive Form. A creature that touches Zargon or hits him with a melee attack while within 5 feet of him takes 14 (4d6) acid damage. Any nonmagical weapon or ammunition made of metal or wood that hits Zargon corrodes and is destroyed instantly.

Foul. Any creature, other than an ooze, that starts its turn within 10 feet of Zargon must succeed on a DC 27 Constitution saving throw or be poisoned until the start of the creature's next turn.

Freedom of Movement. Zargon ignores difficult terrain, and magical effects can't reduce his speed or cause him to be restrained. He can spend 5 feet of movement to escape from nonmagical restraints or being grappled.

God Slayer. Zargon deals double damage to gods and celestials, bypassing their resistances and immunities. If Zargon reduces a god or celestial to 0 hit points, he kills them instantly.

Legendary Resistance (3/Day). If Zargon fails a saving throw, he can choose to succeed instead.

Limited Magic Immunity. Unless he wishes to be affected, Zargon is immune to spells of 4th level or lower. He has advantage on saving throws against all other spells and magical effects.

Magic Weapons. Zargon's weapon attacks are magical.

Regeneration. Zargon regains 25 hit points at the start of his turn. If he takes cold or fire damage, this trait doesn't function at the start of his next turn. Zargon dies only if he starts his turn with 0 hit points and doesn't regenerate.

Slime Trail. Zargon leaves a 5-foot wide trail of slime behind him whenever he swims, climbs, or drags himself forward on the ground. A creature that moves into the slime's space for the first time on a turn or ends its turn there must succeed on a DC 27 Constitution saving throw or take 14 (4d6) acid damage. This slime dissipates 1 minute after being excreted.

Unyielding Essence. Zargon is immune to any spell or effect that would alter his form, as well as those that would read his thoughts, determine if he is lying, or magically influence his thoughts or behavior.

Multiattack. Zargon makes three attacks: one with his gore and two with his barbed tentacles. Alternatively, Zargon makes three attacks with his muscled tendrils. He can replace any melee attack with one use of Fling.

Barbed Tentacle. Melee Weapon Attack: +19 to hit, reach 30 ft., one target. Hit: 19 (2d8 + 10) piercing damage plus 14 (4d6) acid damage, and the target is grappled (escape DC 19).

Muscled Tendril. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage plus 14 (4d6) acid damage, and the target must succeed on a DC 27 Strength saving throw or be knocked prone.

Fling. One Large or smaller object held or creature grappled by Zargon is thrown up to 60 feet in a random direction and knocked prone. If a thrown target strikes a solid surface, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 19 Dexterity saving throw or take the same damage and be knocked prone.

Gore. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 23 (2d12 + 10) piercing damage.

Spew Slime (Recharge 5-6). Zargon spews out corrosive slime in a 60-foot cone. Each creature in the cone must make a DC 27 Constitution saving throw. On a failed save, a creature takes 67 (15d8) acid damage and is poisoned until the start of its next turn. On a successful save, a creature takes half as much damage and is not poisoned.

Zargon 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. Zargon regains spent legendary actions at the start of his turn.

Move. Zargon moves up to half his speed.

Corrupting Touch (Costs 2 Actions). Melee Weapon Attack: +19 to hit, reach 15 ft., one creature. Hit: 24 (4d6 + 10) poison damage, and the target is slimed. Until the slime is scraped off with an action, the target is poisoned, and any creature, other than an ooze, is poisoned while within 10 feet of the target.

Tentacle Swarm (Costs 3 Actions). Zargon unleases the barbed tentacles on one of his arms in a 30-foot cone in front of him. Each creature in the cone must make a DC 27 Strength saving throw, taking 19 (2d8 + 10) piercing damage plus 14 (4d6) acid damage on a failed save, or half as much damage on a successful one. Additionally, up to 6 creatures of Zargon's choice that fail this saving throw are grappled (escape DC 19) by one tentacle each.