Volume 68: Chapter 668-678
Saga 8: Dressrosa
Arc 26: Punk Hazard
4 years ago, Caesar Clown's experiment have failed. Punk Hazard becomes uninhabitated as the poison gas spread to the entire island. He was expelled from World Government. He comes back to Punk Hazard to do a secret experiment as the island cannot be traced by log pose. From the poison gas and chemical substances, he created a monster, Smiley, who ate Sala Sala no Mi Model: Axolotl. Caesar planned to turn Smiley into mass slaughter weapon called Shinokuni. He will sell it in the black market.
Caesar Clown can control oxygen gas so he can suffocated his enemy. Luffy, Robin, Franky, Law, Smoker, Tashigi and other Marines easily defeated by him. Vice Admiral Vergo is Caesar Clown's accomplices. He will cover up all the crime. He also worked for Joker, a black market broker or also known as Donquixote Doflamingo.
Luffy, Law and Smoker join forces to take down Caesar, save the children and escape from Punk Hazard.