Fallen beings who live in a different dimension feed off "dark energy".
They lure humans into contracts with promises of wealth and power.
In exchange they demand certain acts.
These acts vary depending on what is to be achieved.
They always involve "the stealing of innocence".
Once in contract, the beings continually up the stakes.
If the humans try to renegotiate, They beings use fear to keep them in line.
It's a tale as old as time.