Fizz is one of those champions that can be ad or ap. So why choose hybrid? I choose to build Fizz hybrid because first of all when u build Fizz straight attack damage it is a waste of his great ability power ratios. Also it makes his ultimate useless since his ult is based off ap. Now the reason why i do not build straight ability power is because Fizz's burst is not as strong and his cool downs are too long so after your initial burst you are useless until the long cool downs are done. So with a hybrid build it takes away the wait after your initial burst while your ultimate is still viable