In some swamp a witch was doing some experiments on a sewn together body. Got the size and torso from a giant orc, the brain and voice of an elf, genitals from an incubus, the fangs of a vampire, and the stomach of a succubus. The witch theorized that the size and strength of the orc would make her creation physically strong, the elven brain would make you extremely strong and the voice would make you be able to sing and lure people pretty well, the fangs of a vampire plus a few charms could let you drain certain essences from people, and the stomach would make it easier for you to handle/digest the essences... Then the incubus part was just for... Something else. She was doing her incantation to bring the hulking body to life, but she didn't realize that her monster needed a soul to actually come to life. Sadly it was your soul of all souls that entered that thing.
The witch called out "Rise, Rise my creation! We have work to do!"
Rising up from a lab table easily breaking out of the restraints all you could think was "Hungry..." and the vampire and incubus in you saw the witch as an easy snack.
Taking a step towards her the witch said "Yes your working!.. wait stop where you are!!!" as you grabbed her with one arm and bent over and chomped on her neck draining her of her blood as your dick hardened and inserted itself deep in the witch's vagina stealing all her sexual and some magical energies. A second later you stopped and just saw a husk lying on the floor that was the person you guess you could call mommy. You had no memories, but the power you had over that person and the way you just killed her was amazing... You wanted to do more... Looking around the shed you saw your reflection in the mirror. Your face was a bit too pretty, but at least your eyes seemed to glow a weird bright yellow. You looked all over to find something to cover your face and saw an odd mask. It was black with all sorts of weird carvings.
Putting it on thinking "This'll make me look scarier." and then a voice rang out in you "Ah, that witch is gone... what have we here? Some sort of monstrosity?"
You asked "whose there?"
"Oh just a minor evil god trapped in a mask. Say did you enjoy crushing that witch's life and imposing your will and desire onto others?"
"Yes, Can you help me?"
"Sure, I love snuffing out other people's lives... However I think you are strong enough that you don't really need my help killing them. Tell you what though, give me a portion of the essence you steal from the people you kill and i'll do two things for you. First i'll protect you from magic and projectiles."
"Done, I'll start looking."
"Wait big guy! Here's a second part that can make imposing your will a lot funner. It'll take a lot of power, but i'll help make it so you can change people. Heck changing people can help you gain even more essence."
"How so?"
"Well you can sap away age from people which will get you a lot more essence. Besides that they'll got smaller and you can impose your will that much easier, heck you can keep draining till they are just small puddles. Or you could change a man into a woman and do your incubus thing. Or you could change little girls into woman to drain out their sexuality. The sky is the limit, and there are a bunch of cabins around this swamp full of people to kill. If I could make a suggestion how about we go to the..."