What are Renekton's bad matchups?

I'm trying out the freelo machine in normals before going into ranked, a little on my unranked account too for more forgiving matchups. So far I've managed to completely destroy Riven, Nasus, GP. Now I had a little trouble vs Vlad, Fizz, a little bit Liss (that was my fault though, dc'd early). Are these bad matchups or did I play them wrong?
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