Imp

Imp CR: 1

Tiny fiend (devil, shapechanger), lawful evil

Armor Class: 13

Hit Points: 10 3d4+3

Speed: 20 ft , fly: 40 ft

STR

6 -2

DEX

17 +3

CON

13 +1

INT

11 +0

WIS

12 +1

CHA

14 +2

Skills: Deception +4, Insight +3, Persuasion +4, Stealth +5

Damage Resistances: Cold, Bludgeoning, Piercing and Slashing from nonmagical weapons

Damage Immunities: Fire, Poison

Condition Immunities: Poison

Senses: Darkvision 120 ft, passive Perception 11

Languages: Infernal, Common

Challenge Rating: 1

Shapechanger. The imp can use it's action to polymorph into a beast form that resembles a rat (speed 20 ft), a bat (speed 20 ft, fly 60 ft), or a spider (speed 20 ft, climb 20ft), or back into it's true form. It's 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 it's true form if it dies.
Devil's Sight. Magical darkness doesn't impede the imp's Darkvision.
Magic Resistance. The imp has advantage on saving throws against spells or other magical effects.

Actions

Sting. Bite in Beast Form). Melee Weapon Attack +5 to hit, reach 5 ft, one target. Hit 5 1d4+3 piercing damage, and the target must make a DC 11 Constitution saving throw, taking 10 3d6 poison damage on a failed save, or half damage on a successful one.
Invisibility. The imp magically turns invisible until it attacks or until it's concentration ends (as if concentrating on a spell). Any equipment the imp wears or carries is invisible with it.

Horned, winged, with a tail of a scorpion, the imp is the classic devil writ small. It is red and nasty, spiteful, but can be mischievous too.

Suggested Environments

Hell dimensions, and places where it has been summoned or broken through.