Undertale is a role-playing game that utilizes many of the traditional mechanics normally seen in role-playing games but with a number of differences.
The battle system in Undertale is turn-based and seems to be heavily inspired by bullet-hell games – in particular, the Touhou series – where the protagonist’s SOUL, represented by a red heart, must avoid attacks unleashed by the opponent. As the game progresses, new elements are introduced, such as colored obstacles which require the soul to stay still or move through them, and some battles (including some of the Boss battles) which change the way the heart is controlled. During the player’s turn, they have the opportunity to fight the opponent (involving quick-time input), perform actions that can change the opponent’s mood, use items, and show mercy by sparing the enemy, which ends the combat if the correct actions have been used. Killing an enemy will reward EXP and LV, but neither are given if they are successfully spared; GOLD is earned in both cases. The game has a large emphasis on the morality of killing and sparing the Monsters encountered, as the player’s actions determine what ending they will receive. Unlike traditional RPGs, it is possible to complete the game without ever killing a single monster.