One Piece's Wano Country has entered the third act in the manga, and the war with Kaido's forces is only moments away. The 4000 strong rebel army has been gathering together and getting their weapons and armor in order, and part of this army includes some more reinforcements from the Minks of Zou. What this also means is that there's been a tease that the powerful Mink transformation, the Sulong, will be making a return in a future chapter of the series. Given how the couple of transformations seen thus far have been strong on their own, this would be a big deal.
Chapter 959 of the series sees the Minks discuss the potential Sulong transformation playing a key role in the war with Kaido to come, but there's a few caveats as it's going to rely on the weather being clear for the full moon to shine through.
When Luffy and the other Straw Hats are putting the final preparations in order for the upcoming raid on Onigashima, Robin mentioned how it's going to be the Winter in that area. Not only is it going to be cold because Wano's weather varies wildly per region, the weather might just throw a wrench into the Minks' plans. The raid was planned for an attack during the full moon, and as Wanda explains, the Sulong transformation will thus be a thing of luck.
Given that the full moon might be obscured by clouds, the Minks can't rely on the transformation to give them an edge. Although it will be a strong boost to their rebel forces, it's yet another thing that just might not work out. But it's not like they can delay the raid either as this is something that the people of Wano, and Oden's trusted warriors, have been planning for over 20 years now.
An army of Sulong would definitely be great to see in a future chapter of the series, however, and this small conversation is definitely foreshadowing that we'll see at least one Sulong transformation during the Wano Country arc. Series creator Eiichiro Oda is known for little tidbits like this that come to fruition much later when we least expect.
Eiichiro Oda's One Piece first began serialization in Shueisha's Weekly Shonen Jump in 1997. It has since been collected into over 80 volumes, and has been a critical and commercial success worldwide with many of the volumes breaking printing records in Japan. The manga has even set a Guinness World Record for the most copies published for the same comic book by a single author, and is the best-selling manga series worldwide with over 430 million copies sold. The series still ranked number one in manga sales in 2018, which surprised fans of major new entries.