Renan! Experiment 846 3: Time is Important is the third game in the RenarioExtreme series and a sequel to Renan! Experiment 846 2: Dr Mewtwo Returns. This game marks the first appearance of Rexar.
The intro starts with Dr. Mewtwo (with the Mystic Diamonds) heading towards the Guardian Diamond Island, with Renan and Hiroshi in his plane. When Dr. Mewtwo reaches the Guardian Diamond Island, Rexar the Totodile, the guardian of the Guardian Diamond attempts to attack him. To make things worse, Dr. Mewtwo tricks him that Renan and Hiroshi want to steal the Guardian Diamond, so Rexar, after joining Dr. Mewtwo, tries his best to stop them. After Renan defeats Rexar, an earthquake had occured in the island. Rexar then runs to the place of the Guardian Diamond, and was shocked and angry to see Dr. Mewtwo taking the Guardian Diamond. So, Rexar attacks Dr. Mewtwo, but Dr. Mewtwo shakes him away, causing him to fall to the ground. After realized that he has been tricked, Rexar joins Renan and Hiroshi. Before joining them, Rexar asks for forgiveness, which Renan accepts. The Gold Master then takes Renan and Hiroshi to Dr. Mewtwo's Hideout, where Dr. Mewtwo is planning to use the Diamonds to make him become unstoppable. So, Renan, Hiroshi and their new friend Rexar must stop Dr. Mewtwo from taking over the world.