It always demands a sacrifice
It - or - They demand a deal
They are the devil at the crossroads waiting for a soul to steal

The choices of the seven deadly sins
Which one will you choose?

Lust
Gluttony
Greed
Sloth
Wrath
Envy
Pride

It consumes the light, but in return fills with dark pleasure acting as a temporary high; a short-lived fix that like acid burns.