Cetus [5E Monster]

Cetuses are massive, whale-like, marine creatures that typically live far beneath the surface of the sea or far out beyond the sight of land and are therefore only very rarely seen by people. Sometimes, one will become dormant, or even die, and float upon the surface of the water for so long that it becomes covered with sand, flotsam and jetsom, and even vegetation, and either drift or become lodged on reefs. Cetuses that are somehow identified in this condition are typically referred to as "Island Fish," and those that are asleep are sometimes awoken by the activities of the people exploring them (e.g., by those who start bonfires).

Cetus

Gargantuan beast, unaligned

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Armor Class 17 (natural armor)

Hit Points  480 (20d20+180)

Speed Swim 60 ft.

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STR 36(+13)

DEX 8(-1)

CON 28(+9)

INT 3 (-3)

WIS 12(+1)

CHA 2(-4)

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Damage Immunities bludgeoning, piercing, and slashing from nonmagical attacks

Saving Throws Str +17, Con +17

Senses Blindsight (120 ft.), Passive perception 11

Languages --

Challenge  13 (10,00 xp)

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Amphibious The Cetus can breathe air and water.
 

Hibernator The Cetus has disadvantage on saving throws made to resist sleep effects.
 

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

Actions
 

Breach Starting underwater, the Cetus quickly surfaces and capsizes any Huge or smaller ships that are in squares adjacent to it.
 

Swallow A single Huge target, two Large targets, or any number of Medium or smaller targets that are in a 30 ft. cone in front of the Cetus are swallowed. While swallowed, creatures are blinded and restrained, have total cover against attacks and other effects outside the Cetus, and take 14 (4d6) acid damage at the start of each of the Cetus’ turns.

If the Cetus takes 50 damage or more on a single turn from creatures inside it, the Cetus must succeed on a DC 25 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 Cetus. If the Cetus dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 15 feet of movement, exiting prone.

Tail Slap Melee Weapon Attack: +17 to hit, reach 30ft., up to 4 targets in squares adjacent to each other. Hit: 41 (8d6 + 13) bludgeoning damage. Creatures targeted and within 30 ft. of this attack must succeed on a Constitution saving throw (DC 23) or be stunned for 1 round.