One Piece episode 418 is part of the shadow bargain we have with One Piece - they make episodes every week of every year (barring holidays), and we accept the fact that there we will have to watch filler content.
The filler in this episode isn't very heinous, with the exception of a Franky dance number that really goes on way too long. We see Boa Hancock enjoying a wonderful romantic moment with Luffy (in her imagination), which is funny enough to be worth watching. We see Nami again for the first time in months, as she discovers an island that will obviously enhance her weather powers. And, we see Franky with a new power source and a new attitude, which... honestly is about four minutes of wasted time.
One more filler episode, and then it's on to the nonstop thrill ride that is Impel Down!