I am writing this on October 3, 2013, the day after Chapter 723 came out.
So, where to begin? Rebecca's in the arena. Luffy is standing around basically doing nothing. Zoro and Kinemon are standing outside the arena. Doflamingo is attacking the Thousand Sunny. Law has captured Caeser. Fujitora is sitting around. Usopp and Robin are with an army of dwarves that are about to attack Doflamingo. What will happen next? I am so glad that this arc is actually interesting and not boring and long like the past two arcs. Here's what I think will happen from Chapter 724-on
The Arena[]
Rebecca is going to win D Block, hopefully without taking 5 chapters to do so. The next 4 rounds will begin, in which the four victors square off individually against one of the Doflamingo champions. Burgess and Luffy will be able to defeat their competitors, but Bartolomeo and Rebecca will be defeated. Luffy will be crushed when Rebecca is knocked out, but he will be forced to fight Burgess and the two winning Donquixote competitors. Remembering Rebecca's tale, he gets his game back on and manages to defeat Burgess and the two remaining Donquixote fighters. He is then scheduled to face Diamante, but it is announced that the true champion will be facing Luffy instead, as Donquixote Doflamingo enters the arena.
Doflamingo vs. Sanji[]
Back at the Sunny, Sanji and Doflamingo square off. Doflamingo reveals his devil fruit, the Ningyo Ningyo no Mi (Puppet-Puppet Fruit), which lets him control others and himself like puppets. He then takes Nami hostage, and Sanji falters, resulting in him being cut up. Sanji is then played around with, but Brook cuts Doflamingo's strings. However, Doflamingo throws Brook in the water, and Chopper jumps in after him. Sanji and Nami, the only ones who can swim, are bound by Doflamingo, as Brook and Chopper sink into the water. Just then, the Thousand Sunny is beached, right where Usopp, Robin, Franky, and the dwarves are. The Dwarves attack Doflamingo, and Sanji jumps into the water to get Chopper and Brook. Doflamingo easily defeats the dwarves, killing several. However, the massacre stops when he gets a Den Den Mushi call from Diamante, telling him Luffy was in the final four in the arena. Deeming Luffy the greater threat, Doflamingo flys off. The remaining dwarves turn on Usopp, thinking he betrayed them with his promises of glory. However, Sanji comes to them and tells them that they can still get their revenge on Doflamingo if they come with them to the SMILE factory and help them destroy it. The dwarves once again hail Usopp, thanking him for guiding them to Sanjland, the "god of war." The crew then takes the Thousand Sunny back to Dressrosa.
Law, Caesar, and Fujitora[]
When Sanji arrives, Law decides to help him by threatening to kill Caesar, but he is stopped by Fujitora. Fujitora uses gravity to pin Law down, formally revealing his devil fruit, the Genshu Genshu no Mi (Grav-Grav Fruit), which lets him manipulate the force of gravity. Fujitora takes Caesar's heart from Law, and Caesar starts attacking Law. Law manages to avoid Caesar's first few attacks, but the force of the gravity and Caesar's relentless attacks begin to overwhelm him. However, Fujitora gets a call from the Marines saying the Straw Hats have broken into the Corrida Coliseum where the Doflamingo family is, and Fujitora leaves, bringing Caesar with him. However, Law uses room, unbeknowest to them, and switches Caesar's heart with Diamante's, which he had managed to steal back when he worked for Doflamingo.