Kassadin when he had silence he used to be super good, he was the biggest fear of all mid laners and whole team comps, everyone was playing around mid before he reaches 6.
Original Ryze - he was super strong and easy to play. You would have to stack mana and buy some tank items and u would be a monster late game. Nowadays he's total trash and his win rate is total trash.
Fizz - even though he's OK now he has NOTHING on the old fizz and nobody even plays him mid anymore because why would you pick fizz when you can play neeko, sylas, zoe...
AP Tristana - AD Tristana didn't change much but AP Tristana is not even viable nowadays how bad she is. And she use to be one of the biggest fears on mid and top.