I fell the calling to this current. I’m having dreams with Metcalfu. He has even given me veves in my head to draw them. I wish to seek council for I have never worked with this lwa and I understand that you must tread lightly when working with him.
I would ask someone else but they are not into black magic with the same heart as we do.
Any advise of anyone who has worked with him?
If youre being called by a specific entity, I think you can go about approaching them differently than if you are cold calling one. They are expecting you; the offer to work together is actually theirs, which puts you in the position of being able to freely accept or decline. And if you accept, well you are answering THEIR request, so do not need to be as formal as you would if you were doing the requesting, IMO.
I would suggest (with the disclaimer I am not a practitioner of voodoo), to use the veves he has given you, and to make a basic polite offering that is either common to all loa, or specific to him, when you perform whatever ritual you were thinking about performing. Go with what you feel is most appropriate offering wise.
Using the method of approaching any entity with general politeness and respect is a solid tactic for most of them. You could think of it as like contacting a potential business partner.
I suppose you’re talking about Kalfu, most think of him as the opposite of Papa Legba, since they both kinda have similar functions.
just like it’s customary to honor Papa Legba, before the calling of any spirits as he is believed to open the door to the spirit world so it is also believed that Kalfu lets in the demons and other baneful entities from the spirit world.
Most think him to be a dangerous Loa and when he appears in ritual, all fall silent in fear of angering him.
I would say that you approach this just like you would any spirit that you do not know fully. Be wary, be respectful and always have your guard up till you get to know this spirit and it’s intentions, Kalfu may just be misunderstood by a lot of people and it would be cool if you got to know him. I’m very curious as to why he contacted you and I would like to hear about your experiences with him if you do pursue working with him.
~Aluriel
You got it buddy. I intend to.
Go for it ! But don’t be surprised if he decides to test you a bit 
~Aluriel.