EXP System

EXP is the number Undertale's combat raises. Killing an enemy earns the player EXP and gold, and EXP in turn raises their LOVE. The player does not have to kill: by choosing the right actions, or by wearing a monster down without finishing it, they can spare it and end the fight peacefully, and the whole game can be cleared without killing a single enemy. The endings follow from that choice. Killing some or no monsters leads to a Neutral ending, killing none opens the True Pacifist ending, and killing every fightable monster leads to the ending fans call No Mercy or Genocide. Before the human faces Asgore, Sans stops them, reveals that LOVE and EXP stand for "level of violence" and "execution points", and judges them by how much of each they have accumulated.