Well i bought this champ about 5 days ago and, i absolutely love playing mid with her. So far i havn't run into any major counters to her aka Mordekaiser or Swain but i think she matches well with most mid lane champs. One of the few problems i've seen though is her ability to burn mana extremely fast. Leaving you unable to keep fighting sometimes or resulting in death. This is just my two cents on the champ. Comment if you have any suggestions to make me a better Diana or tell me about some counters that could destroy me.