i think this would be a good time to bring the icon back seeing as many players may have not been playing at the time of the icon being available to NA, like myself, and would like the icon. it isn't like it doesn't stick with the theme because Fizz lives in water etc etc
But this is Pool Party Week, and that was Ocean Week. Oceans are bigger than pools, and usually lack the party. Also the icon probably got lost in the middle the ocean... and most importantly:
There is no Pool Party Fizz~
On a more serious note though, icons are usually exclusive timed things that rarely IF ever return after they're gone. There are a few past icons I missed (like the Shurima/Acension for example) that as much I want to come back, it won't. Even if it's slightly related, it probably still won't come back (like the Feijord War and subequent winters)
