First of all, Takashi Miike is insane! Visitor Q still tops my list of movies I wish I had never seen! It was like watching a car crash and not being able to take your eyes away.
Ichi the Killer is extremely over the top. It's like a live action anime. There's so much insane violence, it's almost comical, but still real enough to make you uneasy. The one thing that really bothered me (and I found unnecessary) was the sexual violence. Even if a movie is stylized, I don't need to see that.
I believe his mouth was CGI, Les, but I'm not positive.