Quasit

The monster has Advantage on saving throws against spells and other magical effects.

Melee Attack: +5 to hit. reach 5 ft. Hit: 1d4 + 3 slashing damage.

The monster casts Invisibility on itself, requiring no spell components and using Charisma as the spellcasting ability.

A creature you touch has the Invisible condition until the spell ends. The spell ends early immediately after the target makes an attack roll, deals damage, or casts a spell. Using a Higher-Level Spell Slot. You can target one additional creature for each spell slot level above 2.

The monster shape-shifts to resemble a bat (Speed 10 ft., Fly 40 ft.), a centipede (40 ft., Climb 40 ft.), or a toad (40 ft., Swim 40 ft.), or it returns to its true form. Its game statistics are the same in each form, except for its Speed. Any equipment it is wearing or carrying isn't transformed.

Wisdom Save: DC 10. target: creature.