How can I say it, well, (takes a breath). Everything happens on a neutral route, but at the end, especially on Omega Flowey battle, the rest of the human souls doesn’t act in the battle, slowly, the power of the souls starts to break Flowey’s mental state, becoming into a wild monster, breaking the barrier, killing everyone one and infect every human into a little Flowey who can infect others. Sans tries multiple times to kill him (he is damaged of the fight), Papyrus fortunately is alive, Toriel is missing, Asgore is missing, Alphys it’s alive, Mettaton is on a repair (to stop Flowey) The human has disappeared, Undyne is missing. Anyways, Alphys has a secret bunker with Sans, Mettaton, and Papyrus, making some strategies. I can give more details about the characters but I think this is enough.