Vampiric Werebat

Shapechanger

The werebat can use its action to polymorph into a bat-humanoid hybrid or into a bat, or back into its true form, which is humanoid. Its statistics, other than its AC, are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Echolocation (Bat or Hybrid Form Only)

The werebat can't use its blindsight while deafened.

Keen Hearing

The werebat has advantage on Wisdom (Perception) checks that rely on hearing.

Sunlight Sensitivity

While in sunlight, the werebat has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

 Regeneration

The werebat regains 10 hit points at the start of its turn if it has at least 1 hit point and isn't in sunlight or running water. If the werebat takes radiant damage or damage from holy water, this trait doesn't function at the start of the werebat's next turn.

Blindsight

The werebat has blindsight with a radius of 60 feet.

Multiattack: The werebat makes two attacks, only one of which can be a bite attack.

Claw: Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Bite: Melee Weapon Attack: +7 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the werebat, incapacitated, or restrained. Hit: 8 (1d8 + 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 werebat 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 werebat under the werebat’s control.

Charm: The werebat targets one humanoid it can see within 30 feet of it. If the target can see the werebat, the target must succeed on a DC 14 Wisdom saving throw against this magic or be charmed by the werebat. The charmed target regards the werebat as a trusted friend to be heeded and protected. Although the target isn't under the werebat's control, it takes the werebat's requests or actions in the most favorable way it can. Each time the werebat or the werebat's companions do anything harmful to the target, it can repeat the saving throw, ending the effect on itself on a success. Otherwise, the effect lasts 24 hours or until the werebat is destroyed, is on a different plane of existence than the target, or takes a bonus action to end the effect.

Enter the description for how bonus actions work for your monster here.

Unnerving Dodge When a creature the werebat can see attacks it with an attack, the werebat can use its reaction to impose disadvantage on the attack roll.

The werebat can take 1 legendary action, 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 werebat regains spent legendary actions at the start of its turn.

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

Bite (Costs 2 Actions): The werebat makes a bite attack.