So the episode Time to Get Cereal has brought some to the conclusion that Al Gore was telling the truth the whole time about Manbearpig's existance. Well in my theory, Manbearpig's appearance has instead done the opposite and proves that Al Gore was lying about Manbearpig.
Al Gore had stated many times at the end of the Manbearpig episode that he killed ManbearPig. If he killed Manbearpig in 2006, then why is Manbearpig killing people in 2018? He even made a public announcement about him killing ManBearPig and yet nobody remembers that. Al Gore even thought the New Kid was ManBearPig and attacked him and then later dressed up as ManBearPig and attacked the New Kid again. Though that did not make sense as ManBearPig is not seen to be capable of disguising itself as a full human, since Al Gore asked Stan if his dad had pig hooves in which Stan replies no. The New Kid did not have pig hooves as feet or any features of ManBearPig so that was another slap in the face to Al Gore.
What really was happening was Al Gore did not know ManBearPig was real. He didn't make the demon up, but he thought he had made him up. When the boys came to Al Gore telling him he was right, Al Gore was very shocked in his mind, but he did not want to act surprised or else the boys would know he was lying. So Al Gore went along with it and acted like he was right all along and decided to act stubborn in order to get more attention. He used this technique to make the boys lick his boots and apologize even though it was unnecessary. He may have been able to summon Satan, but anyone was able to do that including Stan who actually did in the Freemium episode. The only thing Al Gore did that was the closest to being helpful was telling the boys that ManBearPig was a demon. But of course anyone could have predicted that and didn't need his help for that. It is unknown why the boys sucked up to Al Gore for help instead of calling him out for bragging about killing ManBearPig when the demon is clearly still alive. Well ManBearPig is no longer a threat for now, no thanks to Al Gore. He never knew about the demon. He didn't have any clue how to defeat it. He just craved attention as always. And that is why ManBearPig's appearance ultimately proves that Al Gore was lying.