First World
The first world is where the original Yuno Gasai originates from. It's events closely follow the timeline of the Second World, with minor differences up until the ending. As there was no 'fake' Yuno Gasai, there would only be two dead bodies. It is unknown whether the bodies were ever discovered. The winner of the Survival Games is Yuno after she and Yukiteru decided on a double suicide. Their method of death were drugs, however Yuno pretended to take them. After she is sure Yukiteru is dead, she spits the pills out and claims her victory as the god of the world.
Second World
Yuno had originally thought that after becoming god she could simply ressurect Yukiteru. However she was unable too. As a solution she travelled to the past, thus creating the Second World. After arriving she slaughters that timeline's Yuno Gasai which meant there were three dead bodies. These are soon discovered by Yukiteru which greatly affects the future. It also creates the suspicion that Yuno is a fake, which in fact she is not, she's taken the Second World's Yuno Gasai's place. In the events of the anime, Aru Akise is constantly warning Yukiteru that Yuno is not to be trusted. After a series of investigating with Masumi Nishijimi, Yuno's secret is discovered.