My first and ONLY monster to beat the Big Four was a second generation Blue Kato, He came out of a not-so-good great combo with my first BK and an unraised Undine, I don't know why, but most of my fair-good monsters turn out to be sub Tigers, Two Blue Katos and a Blue Hare were my some of my only S class monsters, Other than that I had a Black Henger and a Manna get to S.