Imp

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

Melee Attack: +5 to hit. reach 5 ft. Hit: 1d6 + 3 piercing plus 2d6 poison 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 rat (Speed 20 ft.), a raven (20 ft., Fly 60 ft.), or a spider (20 ft., Climb 20 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.