Real Time Mechanics

Real time mechanics are aspects of Undertale that use the computer's current date, time or season to affect gameplay. These aspects can range from aesthetic changes (such as Papyrus's date HUD or the controller configuration screen) to game changing aspects such as So Sorry's appearance.

Papyrus's Date HUD
During the date with Papyrus, the player will press C to open the Date HUD, which consists of a clock, a radar, a crime level graph, a bar with "REEL IT IN!" above it, a population chart and an egg. The date shown on the clock matches the date on the user's computer, and the graphic next to it changes accordingly. The current time has no effect on the date whatsoever.

Controller Configuration Screen
The controller configuration theme changes drastically depending on the season (determined by the computer's clock and location). The overall theme of the screen is themed around whichever season is current, along with seasonal quotes and hats for the Annoying Dog.

So Sorry Boss Battle
So Sorry is a boss that can only be fought if the computer's time is set to October 10th, 8pm. Attempting to fight So Sorry by going to the Art Club room without the proper date set results in So Sorry not showing up at all. So Sorry can be fought at any time by changing the computer's time and not syncing to the internet.