Dorohedroro is getting an anime? Why didn't I know about this? Please, please let it be as amazing as the manga.
There really is no way to explain it well. The main character lives in a giant and lawless city. He has a lizard head. He doesn't know why he had a lizard head or who he really is but if he bites someone else's head, there is a human head inside his mouth that tells him if the biten person is the one he's looking for, presumably to get this real head and life back. Maybe.
Meanwhile, magic users, each one with a particular power, come to his world to experiment on humans. Lots of things going on in the magic user world, where the ruling crime family is having a lot of problems--one of which is that a guy with a lizard head keeps killing their members when they go to the human world.
That's just a very rough starting point. It's violent and imaginative. It's kind of like Berserk if the author was really into writing while experimenting with drugs.