WARNING: The following contains spoilers for One Piece Chapter #1020, "Robin vs. Black Maria," by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English via Manga Plus and Viz Media.
After rescuing Sanji from Black Maria's web a few chapters back in the One Piece manga, Robin and Brook faced the Tobi Roppo member and her followers. Now in Chapter #1020, after the Beast Pirates attempt to use an illusion mist against the two to trick them, Robin squares off against Black Maria alone while Brook takes on her flunkies. This is where Robin unveils what could be the most powerful attack we've seen from her yet: Gigante Fleur. The super move is a step up from her usual attacks, combining not only the powers she was introduced with, but also the ones she developed after the series' time skip.
Robin's powers are all thanks to the Hana Hana no Mi, a Paramecia-type Devil Fruit. Translated as the "Flower Flower Fruit," it allows her to replicate parts of her body and control these replicated parts as if they were a normal part of her body, including eyes, ears, arms, legs, etc.. She's able to create replicants on any surface, including the bodies of other people, as long as they're within range. Unfortunately, these extensions of her body cause her to be more susceptible to touch-type attacks from opponents. Since they are still a part of her natural body, any pain or effects applied to the replicated limbs transfers onto Robin as well, as seen when Sugar turned her into a toy by touching one of her replicated arms.
The most common type of attack she uses is creating multiple arms and using them to attack her opponents. The limbs she replicates aren't limited to the size of her actual limbs, either -- she can create giant versions as well. As of One Piece's time skip, she's also been able to create a clone of herself as well. This is the kind of replication we see during the Onigashima Raid, only to a greater degree, not only using her usual flurry of arms but also creating a net using the replicas of her arm to pull her and Brook to safety. And as she faces Maria in Chapter #1020, she summons possibly the greatest clone we've seen from her so far.
Gigante Fleur has Robin creating a large, multi-armed version of herself. As to what the giant clone does, it's yet to be revealed as the chapter cuts away just as Robin creates it. Since it's the largest clone we've seen so far, this is most likely Robin's ultimate attack. Considering how large Black Maria is by comparison, Robin creating a large clone of herself to combat the Tobi Roppo would be the next logical step for her powers. Perfecting her cloning abilities during the time skip was just the setup she needed to develop this new attack. And if this is the pinnacle of her abilities at this point in One Piece, who knows what else she could do when given the time to develop her powers even further.