fizz seems to counter all mid champs and he is realy good pcik but there are some champions what do you must be afraid of (discribed in last point) you have very big dmg abd trades in early with the most of champions. Yo have to know you must supriseing enemy by useing it in the good moment. your worst stat is your attack range and you must remember to be afraid of range champs and try to dodging their poke.
in midgame yuou must roaming a lot mainly on bottom to getting more feed and in lategame useing your lvl and items what you got in midgame and early. in teamfight you have to throw and r on adc and kill him and after it you are done cause all your work is done