Wellerman (Mimic)

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

Grappler. The mimic has advantage on attack rolls against any creature grappled by it.

 False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from a normal ship.

Animated Ropes. Up to 10 ropes are animated on the deck of the ship. Each rope can be attacked (AC 15; 20 hit points; immunity to poison and psychic damage). For every destroyed rope, Wellerman takes 5 damage. Each round, two new ropes are animated, to a maximum number of 10 ropes. A rope can also be broken if a creature takes an action and succeeds on a DC 15 Strength check against it.

Naval Fortress. Wellerman has different actions depending on the position of enemy. Those can be naval, deck and below deck.

Bite (Naval Only). Wellerman bites down with its bow. Each creature in a 20ft cone in front of Wellerman must make a DC 18 Dexterity saving throw. If its a large or smaller creature and fails the save, it is swallowed. The swallowed creature is then moved below the deck of the ship. If its a huge or bigger creature, it instead takes the same damage as if it was a naval vehicle. Naval vehicles automatically fail the saving throw, taking 66 (12d10) piercing damage.

Ram (Naval Only). Wellerman makes a charge attack, moving up to half its total movement speed in a straight line and crashing into any enemy or vehicle in its path with its ram. Each creature in its path makes a DC 18 Dexterity saving throw and takes 35 (10d6) bludgeoning damage, or half as much on a succesful save. The charge stops shortly if it hits a naval vehicle, against which it makes a melee attack +14 against the AC of the part of the ship which it hit. If it hits, it deals 35 (10d6) bludgeoning damage and 10 ropes shoot out from the front of Wellerman, restraining itself and the naval vehicle. To escape the restrain, ropes have to be destroyed, each having 20 Hit Points and 15 AC. Destroying a rope deals 5 damage to Wellerman. The damage of a Bite attack against a naval vehicle restrained in this way is doubled. 

Cannon Barrage - 4 attacks (Naval Only). Ranged Weapon Attack: +6 to hit, range 600/2400 ft., one target. Hit: 44 (8d10) bludgeoning damage. Each succesful attack spawns a mimic in form of a cannon ball on the part of the ship that got hit by that attack.

Grasping Ropes (Deck Only). Wellerman makes three Grasping Ropes melee attacks +14 to hit, against three different creatures on its deck. Hit: The target is grappled (escape DC 18). Until the grapple ends, the target is restrained and has disadvantage on Strength checks and Strength saving throws, and the Wellerman can't use the same rope on another target.

Splintered Pseudopod (Deck and Below Deck Only). Wellerman can lash out with its pseudopods formed out of materials found on the ship, such as entangled ropes, splintered wood or broken furniture.
Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 21 (3d8 + 7) bludgeoning damage. If the creature hit by the Pseudopod is grappled or restrained, it deals one additional damage die.

Animated Objects (Deck and Below Deck Only). Up to 4 objects on the deck or below deck animate and attack. Use mimic's stat block for these object, but replace AC, DC and attack bonus with those of Wellerman. For every destroyed mimic animated in this way, Wellerman takes 20 damage.

Swallowing Deck (Deck and Below Deck Only). The floor in a 15ft radius opens up and swallows anything standing on top of it. Each creature must make a DC18 Dexterity saving throw or be swallowed. A creature that fails the saving throw receives 21 (6d6) piercing damage and if it stands on the deck, it is moved below the deck. A creature that is swallowed below the deck is instead restrained (escape DC 18). On a success, the damage is halved and the creature is not swallowed.

Multiple Reactions. Wellerman has three reactions per round, but can only use one per turn and only one per creature.

Ever-present Opportunity. Anytime a creature moves above or below deck, Wellerman can use its reaction to make an opportunity attack, picking one of the possibilities:

Cannonball. A stored cannonball is hurled against the creature from a point of DM's choosing. The cannonball flies in a straight line up to 90 feet in creature's direction before falling to the ground, stopping early if it impacts against a solid surface. If the cannonball would strike a creature, that creature must make a DC 18 Dexterity saving throw. On a failed save, the object strikes the target and knocks it prone, dealing 18 (4d8) bludgeoning damage.

Rope Lash. A rope lashes out at the creature from the point of DM's choosing. A creature must make a DC 18 Dexterity Saving Throw or be grappled by it. A creature can escape the grapple as normal or break the rope (AC 15, 20 hit points).

Wellerman can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Wellerman regains spent legendary actions at the start of its turn.

Grasping Ropes. Wellerman makes a Grasping Ropes attack, attacking with two ropes instead of three.

Splintered Pseudopod. Wellerman makes one Splintered Pseudopod attack.

Animated Mimic (Costs 2 actions) Wellerman uses his Animated Objects attack, creating 2 mimics instead of 4.

Cannon Attack - 2 attacks (Costs 2 actions). Wellerman uses his Cannon Barrage attack, shooting 2 cannonballs instead of 4.

Swallowing Deck (Costs 3 actions). Wellerman uses its Swallowing Deck ability.