I worked very in depth with Beelzebub for about 8 months straight, and from what I’ve gathered (by his direct admission) he told me that he is Marduk, Bael, Bel, Baalzeboul, Beelzebuth, Baal Zebub, the Apostle Jude, and Amon-Ra.
He is very kind but sometimes brutally honest. His voice sounds like a roaring furnace, planets being ripped apart, thousands of unearthly motors, and more gutteral than the human voice is capable. In my experience he is roughly 7 feet tall, huge muscles, skin blacker than the Abyss itself, totally naked, eyes are holes in his head that fire comes out always, when he opens his mouth this internal fire is breathed out as well, two large curvy black horns, black cloven hooves, and fingers like claws.
For me, his initial essence was the feeling of falling into damnation itself, a feeling like I was going to vomit, urinate, and defecate all at once, like being in the presence of royalty that could have me destroyed in the blink of an eye if he wanted, but after we got to know each other, he became my closest spiritual friend, Brother, ally, and mentor, and his essence changed from a terrifying chaotic darkness, to a beautiful, protective, friendly chaotic darkness. When he would do something in my life, there would be a feel to that event that is difficult to explain, yet unmistakable and unlike any other feeling I’ve ever experienced, you just know when his hand is in something.
As far as offerings go, all he would ever have me give him was sage (this was rare); if you want to enter into a pact with him, all he asked of me was total, unwavering devotion to my personal ascent, all he wants is for you to care about yourself enough to do as he says (he gives some of the best advice I’ve ever received, like a grandfather/friend/brother all in one, he’s honestly amazing).
The sigil I used to contact him (on his request) was the sigil of Bael from the Goetia.
If you end up working with him (which I STRONGLY urge you to do) ask him about revealing some of his spiritual initiations to you, he will always deliver with some intensely powerful rituals which yield some utterly terrifying and awe inspiring results!
I hope this helps! If you have any questions about my experiences with him, just ask!