Oscar aka O Scar was Catalina's nephew who supposedly possessed voodoo powers.
Oscar came to visit America via a box, similar to how Catalina first arrived. He stayed with Catalina, but Randy offered to look after him in the hopes of proving to Earl he could be a good big brother. Catalina quickly accepted.
When Oscar stole some money from the Crab Shack, Randy tried to tell him that what he did was wrong. Oscar became angered and started to speak gibberish, scaring Randy. Randy told Earl what happened, who told Catalina. She explained that he never did as he was told as he possessed voodoo powers, which Earl thought was nonsense.
Joy later witnessed Oscar's powers, which she also attributed to voodoo. She brought a mob of people to deal with Oscar, but thanks to Earl's karma the crisis was averted. When Earl explained this to Oscar, he refused to believe in Earl's concept, stating that he simply made sure he was not harmed himself ("Little Bad Voodoo Brother").