How do you say bad as hill in Spanish?

I don't know why you'd want to say that, because it will just be confusing to any Spanish speakers who don't also know English. Unlike English, in Spanish the Word for Hell (el infierno) doesn't sound anything like the Word for hill (la colina).

"Bad as" is "Malo como", though. You should be able to construct whatever it was you wanted to say from that information.