Quasit

The quasit is resistant to cold, fire, and lightning damage. In addition, it is immune to poison damage and to the poisoned condition.

The quasit has advantage on saving throws against spells and other magical effects.

Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4+3) piercing damage, and the target must succeed on a DC 13 Constitution saving throw or take 5 (2d4) poison damage and be poisoned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

The quasit magically turns invisible until it attacks, uses Scare, or uses Change Shape, or until its concentration ends (as if concentrating on a spell). Any equipment the quasit wears or carries is invisible with it.

Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6+3) bludgeoning, piercing, or slashing damage (based on the type of damage dealt by the Beast form's primary attack, such as Bite).

The quasit magically transforms into a Medium or smaller Beast that has a CR no higher than its own or back into its true form, which is a Fiend. Its statistics, other than its size and speed, are the same in each form.
Any equipment it is wearing or carrying transforms with it. It reverts to its true form if it dies.

One creature of the quasit's choice within 20 feet of it must succeed on a DC 13 Wisdom saving throw or be frightened for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.