Cephalo-Ship

Amphibious. The cephalo-ship can breathe air and water.

Freedom of Movement. The cephalo-ship ignores difficult terrain, and magical effects can't reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled.

False Appearance. While the cephalo-ship keeps its tentacles underwater, it is indistinguishable from a normal warship. 

Hull Armor. The cephalo-ship wears the hull of a warship like armor, limiting its movement and attacks but providing protection. It has a damage threshold of 20, an armor class of 15, and 500 hit points. If the hull takes damage below the threshold, it is not consequential enough to deal significant damage. While the hull armor is intact, the cephalo-ship can move up to its speed straight forward with one 90 degree turn every turn

Siege Monster. The cephalo-ship deals double damage to objects and structures.

Warship. Until the hull armor is destroyed, the cephalo-ship is treated like a Warship, but lacking sails and oars, propelling itself with 8 giant tentacles.

Multiattack. While the cephalo-ship has its hull armor and a crew, it can take 3 actions, choosing from the warship options below. It can take only 2 actions if it has fewer than twenty crew and only 1 action if it has fewer than ten. It can't take these actions if it has fewer than three crew, at which point the cephalo-ship will leave its hull armor make three attacks, choosing from the unarmored options below.

Ballista(2) (Warship only). Armor Class 15. Hit Points 50 each. Ranged Weapon Attack: +6 to hit, range 120/480 ft., one target. Hit: 16 (3d10) piercing damage

Cannon(2) (Warship only). Armor Class 19. Hit Points 75 each. Ranged Weapon Attack: +6 to hit, range 600/2,400 ft., one target. Hit: 44 (8d10) bludgeoning damage.

Naval Ram (Warship only). Armor Class 20. Hit Points 100 (damage threshold 10). The warship armor has advantage on all saving throws relating to crashing when it crashes into a creature or an object. Any damage it takes from the crash is applied to the naval ram rather than to the ship. These benefits don't apply if another vessel crashes into the warship armor.

Bite (Unarmored only). Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) piercing damage.

If the target is a Large or smaller creature grappled by the cephalo-ship, that creature 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 cephalo-ship, and it takes 21 (6d6) acid damage at the start of each of the cephalo-ship’s turns. If the cephalo-ship takes 35 damage or more on a single turn from a creature inside it, the cephalo-ship must succeed on a DC 23 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in spaces within 10 feet of the cephalo-ship. If the cephalo-ship dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 10 feet of movement, exiting prone.

Tentacle (Unarmored only). Melee Weapon Attack: +12 to hit, reach 20 ft., one target. Hit: 17 (3d6 + 7) bludgeoning damage, and the target is grappled (escape DC 20). Until the grapple ends, the target is restrained. The cephalo-ship has 8 tentacles, each of which can grapple one target.

Fling (Unarmored only). One Large or smaller object held or creature grappled by the kraken is thrown up to 40 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 13 Dexterity saving throw or take the same damage and be knocked prone.

The cephalo-ship can take 1 legendary action. The legendary action can only happen at the end of another creature's turn, but can be used while wearing the hull armor or not. The cephalo-ship regains its legendary action at the start of its turn.

Ink Cloud. While underwater, the cephalo-ship expels an ink cloud in a 40-foot radius. The cloud spreads around corners, and that area is heavily obscured to creatures other than the cephalo-ship. Each creature other than the cephalo-ship that ends its turn there must succeed on a DC 18 Constitution saving throw, taking 11 (2d10) poison damage on a failed save or half as much damage on a successful one. A strong current disperses the cloud, which otherwise disappears at the end of the cephalo-ship’s next turn.