Legion, The Demon Who Is Many
If an unrepentant sinner were to keep graven likenesses or images and find themselves in Hell, the unfortunate soul may meet Legion. While you may have heard someone on 4chan mention that they "are Legion," the real demon appears in the Bible, encountering Jesus at one point in his travels. Taking over the body of a man, Legion is actually a group of demonic entities. The being begs Jesus to be left alone, but the messiah performs an exorcism and sends the vile beast(s) back to Hell.
This will give you a portal to this demon. Again, this is not for the beginner companion, and sometimes not for the experienced. this requires a seasoned Companion