Crypt-Scamp

Nocturnal Shift. The Crypt-Scamp can use its action to polymorph into a bat (speed 10 ft. fly 60 ft.) and back into its true form. Its statistics are the same in each form, except for the speed changes noted. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Grave-Stone Hide. The Crypt-Scamp has advantage on saving throws against spells and other magical effects, and resistance to non-magical bludgeoning, piercing, and slashing damage.

Stone-Sentinel. The Crypt-Scamp settles onto a surface and remains motionless while its skin turns stonelike, becoming indistinguishable from an inanimate statue. While in this state, it cannot move or take actions (except to end this state as a bonus action). It gains the following benefits:

• Mason's Deceit. It automatically succeeds on any Dexterity (Stealth) check to hide. It cannot be detected as a creature by simple spells such as See Invisibility or Detect Magic, which would only register it as a non-magical statue. True Sight or a successful Intelligence (Investigation) check can however reveal its true nature.
• Grave-Sense. It gains Tremorsense out to a range of 60 feet. 

Sanguine Claw. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) piercing damage, and the target must succeed on a DC 14 Constitution saving throw or be unable to regain hit points until the start of the Crypt-Scamp's next turn.

Vexing Visage (1/Day). As an action, the Crypt-Scamp can contort its features into a horrifying gargoyle-esque expression. One creature of its choice within 20 feet that can see it must succeed on a DC 14 Wisdom saving throw or become frightened of the Crypt-Scamp for 1 minute. The frightened target can repeat the saving throw at the end of each of its turns, ending the effect on a success. 

Invisibility. The Crypt-Scamp magically turns invisible until it attacks or uses Vexing Visage, or until its concentration ends (as if concentrating on a spell). Any equipment the quasit wears or carries is invisible with it.