EXPLANATIONS:
The Roaring: The Knight causes The Roaring, turning all the darkners into stone and unleashing the titans. The lightners must come under one banner and pull their last stand.
Social Darwinism: The secret bosses from each chapter somehow come back, sending the Dark World into chaos and under one motto: It’s kill or be killed.
Spamtonia: Spamton successfully kills Kris and absorbs their soul in the Snowgrave Route. He imprisons Queen and the rest of the Fun Gang and sets up a totalitarian plutocracy, where he rules the Cyber World with an iron fist.
Frozen Heart: Susie rejects Noelle, which breaks Noelle’s heart and gradually sends her into a path of malice and lots of people frozen to death.
Evil Ralsei: Ralsei betrays the Fun Gang, revealing that he was the knight this whole time, or at least related to them.
SNOWGRAVE: More Snowgrave routes appear in the later chapters. If all of them are complete, Noelle would have enough and you fight her as a boss.
Very, Very, Interesting: Gaster was revealed to be in the bunker, and the knight was nothing but a rumor. He wanted to create a game as his experiment, which is why he implanted the soul into Kris and invented the dark fountain.
Inner Demons: Kris has enough of being controlled by the soul and breaks free once and for all, no longer bounded to it. Mysteriously, the vessel you created at the beginning of the game is provided for the soul after Kris breaks free. The two of you would confront and have a battle.
Merge of Worlds: The light world and the dark world combines to form one unified world. Thats literally it.
Arf: The Annoying Dog absorbs the entire Deltarune universe after the completion of chapter 3. It was all just an elaborate troll.
Nubert Fan Club: There is no ending, only your homie Nubert.
Sins of the Father: Somewhere later in the game, King gains a redemption arc. It ultimately ends with King sacrificing himself for Queen and Lancer.
King of the Dark: Ralsei finally changes his name to be the king after all of the darkners are brought to Castle Town.
Rehabilitation: After completing the main story, you have an option to play more to help the secret bosses regain their sanity.
God Has Other Plans: Toby Fox dies before he is able to complete Deltarune.
Seriously: All of the major foreshadowings in the game, such as the bunker or the knight, leads up to nothing.
Eradication: Everyone dies in the end. That’s literally it.
