Diabolical Stalker

Whether obsessed with a single unattainable target, or simply loving the thrill of the hunt, some would trade their souls for diabolical powers and supernatural boons. The Diabolical Stalker has traded flesh with a devilish imp, binding both together in a magical pact likely to doom the ranger’s soul to the Nine Hells of Baator.

DIABOLICAL STALKER SPELLS
3rd Hellish Rebuke
5th Zone of Truth
9th Magic Circle
13th Greater Invisibility
17th Planar Binding

Imp Companion

At 3rd level, as an action, you can magically summon the imp that is bound to you. It appears in an unoccupied space of your choice within 30 feet of you. The imp is friendly to you and your companions, and it obeys your commands. See its game statistics in the accompanying Imp Companion stat block, which uses your proficiency bonus (PB) in several places.

While your imp is on the same plane of existence, you can communicate with it telepathically. Additionally, as an action, you can see through your imp's eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses that the imp has. During this time, you are deaf and blind with regard to your own senses.

In combat, the imp shares your initiative count, but it takes its turn immediately after yours. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to telepathically command it to take another action. That action can be one in its stat block or some other action. If you are incapacitated, the imp can take any action of its choice, not just Dodge.

The imp remains until it is reduced to 0 hit points, until you use this feature to summon the imp again, or until you die. Anything the imp was wearing or carrying is left behind when the imp vanishes. Once you summon the imp, you can’t do so again until you finish a long rest, unless you expend a spell slot of 1st level or higher to summon it.

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IMP COMPANION

Tiny Fiend

Armor Class: 13 + PB (natural armor)

Hit Points: 3 + three times your ranger level (the drake has a number of Hit Dice [d6s] equal to your ranger level)

Speed: 20 ft. Fly 40 ft.

STR 6 (-2) DEX 17 (+3) CON 13 (+1) INT 11 (+0) WIS 12 (+1) CHA 14 (+2)

Saving Throws: Dex +3 plus PB, Cha +2 plus PB

Skills:  Insight +3, Perception +3, Sleight of Hand +5, Stealth +5

Damage Immunities: Fire, Poison

Condition Immunities: Poisoned

Damage Resistances: cold; bludgeoning, piercing, and slashing from non-magical weapons that aren't silvered

Senses: darkvision 120 ft., passive Perception 13

Languages: Common, Infernal, any language the ranger understands

Shapechanger. The imp can use its action to polymorph into a beast form that resembles a rat (speed 20ft.), a raven (20ft., fly 60ft.), or a spider (20ft., climb 20ft.), or 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.

Devil's Sight. Magical darkness doesn't impede the imp's darkvision.

Magic Resistance. The imp has advantage on saving throws against spells and other magical effects.

Actions

Sting (Bite in Beast Form). Melee Weapon Attack: +3 plus PB to hit, reach 5 ft, one target. Hit: 1d4 + 3 piercing damage, and the target must make on a Constitution saving throw (your spell-save DC), taking 3d6 poison damage on a failed save, or half as much damage on a successful one.

Invisibility. The imp magically turns invisible until it attacks or until its concentration ends (as if concentrating on a spell). Any equipment the imp wears or carries is invisible with it.

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Devilish Whispers

The telepathic connection to an intelligent creature from another plane of existence has lent you some insight most would consider unnatural.  

Guidance. You learn the Guidance cantrip, which is a ranger spell for you.

Tongue of Devils. You learn to speak, read, and write Infernal or one other language of your choice.

Bond of Fire and Brimstone

At 7th level, the bond you share with your imp intensifies, protecting you and lending it additional skill in combat.

While your imp is summoned, you and the imp gain the following benefits:

Surprise Attack. The imp’s Sting or Bite attack deals an extra 1d6 damage against any target which cannot see it or is adjacent to you, and scores a Critical Hit on a 19 or 20.

Shared Resistance. You have advantage on saving throws against spells and other magical effects, and gain resistance to one damage type chosen from the Imp’s Immunities and Resistances. (Fire, Poison, Cold, Bludgeoning, Piercing, or Slashing weapons which are non-magical nor silvered)

Hellish Expulsion

At 11th level, as an action, you can exhale a 30-foot cone of damaging breath or cause your imp to exhale it. Choose cold, fire, or poison damage (your choice doesn’t have to match your Shared Resistance). Each creature in the cone must make a Dexterity saving throw against your spellsave DC, taking 8d6 damage on a failed save, or half as much damage on a successful one.

This damage increases to 10d6 when you reach 15th level in this class. Once you use this feature, you can’t do so again until you finish a long rest, unless you expend a spell slot of 3rd level or higher to use it again.

Intertwined Existence

At 15th level, your bond to your imp reaches the pinnacle of its power. While your imp is summoned, you and the imp gain the following benefits:

Envenomed attacks. Weapons you wield become coated with Imp venom, dealing an additional 3d6 poison damage on a successful hit.

Warrior Imp. When your imp makes a melee Bite or Sting attack action, it attacks twice.

Reflexive Avoidance. When either you or the imp is struck by an attack you can see, you can use your reaction to swap places so long as you are on the same plane of existence, possibly causing the attack to miss (particularly if your imp is invisible). You can use this reaction a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.