Shapechanger. The can  it can use its action, to polymorph into a Tiny leech or a Medium cloud of slime, or back into its true form.

While in Leech form, the vampire can’t speak, its walking speed is 5 feet, and it has a swim speed of 60 feet. Its statistics, other than its size and speed, are unchanged. Anything it is wearing transforms with it, but nothing it is carrying does. It reverts to its true form if it dies.

While in slime form, the vampire can’t take any actions, speak, or manipulate objects. It is weightless, has a swim speed of 120ft, can hover, and can enter a hostile creature’s space and stop there. In addition, if air can pass through a space, the slime can do so without squeezing. It has advantage on Strength, Dexterity, and Constitution saving throws, and it is immune to all nonmagical damage.

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

slimy Escape. When it drops to 0 hit points outside its resting place, the vampire transforms into a cloud of slime (as in the Shapechanger trait) instead of falling unconscious,

While it has 0 hit points in mist form, it can’t revert to its vampire form, and it must reach its resting place within 2 hours or be destroyed. Once in its resting place, it reverts to its vampire form. It is then paralyzed until it regains at least 1 hit point. After spending 1 hour in its resting place with 0 hit points, it regains 1 hit point.

Regeneration. The vampire regains 20 hit points at the start of its turn if it has at least 1 hit point . If the vampire takes radiant damage or damage from holy water, this trait doesn’t function at the start of the vampire’s next turn.

Spider Climb. The vampire can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Vampire Weaknesses. The vampire has the following flaws:

Forbiddance. The vampire can’t enter a residence without an invitation from one of the occupants.

 Stake to the Heart. If a piercing weapon made of wood is driven into the vampire’s heart while the vampire is incapacitated in its resting place, the vampire is paralyzed until the stake is removed.

Sunlight sensitivity.While in sunlight,the vampire has disadvantage on attack rolls,and take 20 radiant damage at the start of each of their turns.

Amphibious

The vampire can breath both air and water.

Multiattack. (Vampire Form Only). The vampire makes two attacks, only one of which can be a bite attack.

Unarmed Strike (Vampire Form Only). Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 8 (1d8 + 4) bludgeoning damage. Instead of dealing damage, the vampire can grapple the target (escape DC 18).

Bite. (leech or Vampire Form Only). Melee Weapon Attack: +9 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the vampire, incapacitated, or restrained. Hit: 7 (1d6 + 4) piercing damage plus 10 (3d6) necrotic damage. The target’s hit point maximum is reduced by an amount equal to the necrotic damage taken, and the vampire regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. A humanoid slain in this way and then buried in the ground rises the following night as a deep vampire spawn, under the vampire’s control.

Children of the Deep(1/Day). The vampire magically calls 2d4  Swarm of quippers,  While outdoors, the vampire can call 3d6 hunter sharks instead. The called creatures arrive in 1d4 rounds, acting as allies of the vampire and obeying its spoken commands. The beasts remain for 1 hour, until the vampire dies, or until the vampire dismisses them as a bonus action.

Terror of the deep (recharge 6)

The vampire chooses one creature within 30ft of it.That creature must make a dc 18 wisdom saving throw,or be frightened for 1 minute.While frightened in this way,it's swim speed,if any,is considered 0.The creature can reattempt the save as an action,ending the effect on a success.

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

Move. The vampire moves up to its speed without provoking opportunity attacks.

Unarmed Strike. The vampire makes one unarmed strike.

Terror of the deep The vampire uses the terror the deep action,or recharges it if it is unavailable.