Spoiler: In chapter 980 suddenly Monet and Vergo reappear on the Sunny. They've been there the entire time.
In chapter 981 Pedro joins the alliance out of nowhere and Perospero reveals, that he actually didn't lose an arm. It was an optical illusion.
That only gets topped by chapter 982, when Ace makes a shocking return, explaining that he just faked his death in order to end the war.
This leads to a totally unexpected WB entrance in chapter 983, where he explains that this was his masterplan all along and that thankfully nobody died in the war.
Fans think that was it, when at the end of chapter 984 suddenly Oden and Toki resurface and confront WB, telling him that they missed him and that they were his partners all along.