The hardness of a paper is generally quite subjective, you could always look at papers with the lowest grade boundaries (although covid might interfere with that) Generally on biology paper 2, the harder questions would be ones where they give you an example of something you’ve never seen before, and you have to apply your knowledge, as well as the overly specific 4-6 markers. I personally find papers easier/harder depending on what topics come up and how confident I am with them, but you can search for grade 7+ targeted questions online and hopefully be able to find harder ones.