This Walkthrough will take you through Undertale on a Genocide run. This requires you to not only kill every character you come across but to actively continue searching in areas until you’ve killed every possible random encounter to get a unique ending. You will, however, not have to complete most of the puzzles.
Note: Completing a genocide run will alter your save file for future playthroughs. If you want to experience all endings it is recommended you play a Pacifist run first using our Pacifist Walkthrough.
Before the game starts a brief series of cutscenes will explain the history of the world you are about to enter. These scenes tell of a war between humans and monsters where monsters were forced to live in the Underground located beneath the Earth’s surface. It will finish with images of a child falling into the deep hole which leads to the aforementioned world.
This child happens to be you, so give yourself a name and head out of the room to the right to begin your adventure. (on PC you use arrow keys, not WASD to move).
In Undertale you will make your way through different as you try to escape the Underground. The first area you’ll encounter is the Ruins.