Vanislaad

Vanislaad, also known as incubus/succubus or children of Vanislaas, are infernal undead and empathy demons. They are highly cunning and manipulative, especially compared to other demons, such that the proper recommended way to handle one is to avoid all contact. In their true form they have wings and a tail, garnet-colored eyes and alabaster skin. They can shapeshift into all types of human forms, fly, and become invisible. They use these to infiltrate among humans and seduce and corrupt them, as this is the way their infernal corruption expresses itself.

They are formed when a human soul is sent to Hell and manages to impress Prince Vanislaas where he then makes a body out of infernal magic for it inhabit (this is why they are technically undead and so vulnerable to valkyries). This process allows to be effectively immortal, as they can be remade and return to the mortal plane when summoned again.

While the summoning ritual is very easy to do, it is very illegal and getting the instructions would require black market connections.