Demonic Invoker

Demonic Invokers are a rare breed, born with the power to reach out to hell and draw its foul denizens into the bodies of slain mankind. Your people are commanders of vast ashen armies and the consorts of dark lords in need of an army. 
You may have started with the corpses of small animals or, in a desperate defense, rose unholy creatures in a time of panic. In either case, there is further artistry that comes with forging devils into flesh and calling forth an old magic only attained by blood right.

Invoker's Magic

Your abilities are an affront to the divine, and yet its adjacence allows you to draw from its magic as your own. When your Spellcasting feature lets you learn or replace a sorcerer cantrip or a sorcerer spell of 1st level or higher, you can choose the new spell from the cleric spell list or the sorcerer spell list. You must otherwise obey all the restrictions for selecting the spell, and it becomes a sorcerer spell for you.

Demonic Companion

Your power over demons and death has yielded a companion, a demon inhabiting once dead flesh. It is friendly to you and your companions, and it obeys your commands. See this creature’s game statistics in the Demonic Invokee stat block, which uses your proficiency bonus (PB) in several places. You determine the creature’s appearance and whether it has two legs or four; your choice has no effect on its game statistics.

In combat, the invokee 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 command it to take another action. That action can be one in its stat block or some other action. If you are incapacitated, the invokee can take any action of its choice, not just Dodge.

If it has died within the last hour, you can use your arcane focus as an action to revive it, provided you are within 5 feet of it and you expend a spell slot of 1st level or higher. The steel defender returns to life after 1 minute with all its hit points restored.

At the end of a long rest, you can create a new invokee if you have your arcane focus and the corpse of a Medium or Small creature with you. If you already have a invokee from this feature, the first one immediately perishes. The invokee also perishes if you die.

Empowered Invoking

Starting at 6th level, your proficiency with populating corpses with the spirits of demons increases. Creatures you raise with animate dead and create undead gain resistance to fire and cold damage. You add your proficiency bonus to the hit points and damage of undead you control and they are considered fiends for the purpose of class features features. 

For your Demonic Companion, it instead gains an additional half your proficiency bonus to its hit points and damage. You can spend 2 sorcery points to give it a flying speed of 40 feet for 24 hours.

Combat Invoking

When you reach 14th level, you can invoke demons into dead flesh almost instantly after slaying a foe. When you kill a humanoid within 5 feet, you can immediately cast the animate dead spell on it as a bonus action, provided you have a spell slot with which to cast it. You can cast animate dead as an action.

Invoker's Mastery

At 18th level, you master the art of grafting demon to flesh and can choose the form of your creations. You can spend 6 sorcery points as a bonus action to turn an undead or fiend you control into a gargoyle, ogre or saber-toothed tiger. You replace the creature's resistances and immunities with those of the zombie before adding the benefits of your Empowered Invoking feature.

An undead or fiend affected by this feature return to its original state once you finish a short rest.