Is ONE PIECE episode 665 filler?
Canon No, episode 665 of ONE PIECE is canon.
#665
A Burning Passion! Rebecca vs. Suleiman!
熱き思い レベッカＶＳスレイマン
Aired 12 Oct 2014
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.