Even with Deltarune Chapters 1-4 already out, creator Toby Fox is still hard at work. When he isn’t busy fixing bugs and glitches, he wants to ensure players are having fun and experiencing all that the game has to offer. Fox even has a hint for those who think they have seen everything after completing Chapter 4.
This hint seems to point to some post-completion content. Be sure to check your Castle Town, its Recruits, as well as your Inventory and Storage (the last three of which can be done from any save point). If you haven’t seen any changes, try backtracking and talking to the NPCs. Seeing as many people have yet to complete Chapter 4 (myself included), Fox was kind enough to leave out spoilers in his hint.
Deltarune Chapters 1-4 is now available for Nintendo Switch 1 and 2, PC (macOS and Windows), and PlayStation 4 and 5.