"After the events of the first game, Robotnik would begin cleaning up his base of operations after Sonic wrecked it when he stumbled upon the corpse of a flicky that had been heavily charred on account of damage done by a badnik. Although he was put off by the thought of taking a bit for curiosity's sake, the aroma coming from the corpse intrigued Robotnik, and he took a careful bite from the flicky. Immediately after taking a bite from the flicky, Robotnik became enamoured by its euphoric taste. Afterwards, Robotnik took the flicky corpse and savoured it for a few days. No longer wanting to take over the world and go after the Chaos Emeralds, Robotnik now desired to satisfy his insatiable hunger in the only way he knew how: consuming the flesh of mobians. Soon enough, Robotnik began to refurbish his badniks into making them able to kidnap and cook flickies inside of them. He also began construction on his latest creation: Furnace, a metal sonic replica that could keep up with Sonic's speed and snatch up unsuspecting prey to cook and deliver back to him. However, on account of his newfound diet, Robotnik began to suffer the debilitating consequences. His skin would swell and redden and his mustache hairs would gradually begin falling out. A foul stench would also begin emitting from him. Eventually, Robotnik launched an attack on Little Planet and began his enslavement of it, forcing Sonic to face him once more. At one point, he met a pink hedgehog named Amy Rose, who was infatuated with him. However, the moment was cut short when Furnace intervened and kills Amy on the spot by grabbing her and throwing her inside his chest cavity. Sonic watched in horror as he heard Amy scream from being incinerated and her bones crack. Sonic would later confront Furnace at Stardust Speedway, with the latter challenging him to a race. As the race began, Sonic managed to quickly outpace Furnace as Robotnik observed and eventually caught up to him. As Sonic began taunting Robotnik, Furnace raced to the end and set up a trap for Sonic, placing a wall of spikes at the finish line. Once Sonic saw Robotnik slow down, he figured that he had won until he collided face-first with the wall of spikes, killing him instantly. Overjoyed to have finally killed Sonic, Robotnik took his corpse back to his lair and kept him as a trophy to eat on special occasions, relishing in the fact that he was finally able to eat the one thing he desired most. Afterwards, Robotnik managed to gain hold of the Time Stones and decided to use them to continue to infinitely feed for as long as he could. However, his plans were put in jeopardy when he discovered Tails, a fox that was beginning to fight back against Robotnik and that he had previously encountered, but not yet consumed, and now greatly desired to do so."
uberduck.ai for Scout's explanation.
