UNDERTALE

The game casts players in the role of a child as they explore an underground world full of monsters who they can either kill or befriend. The overworld lets the player navigate in a top-down perspective, visiting locations such as towns, shops, and large buildings. Progression through the game requires interacting with puzzles and non-player characters, moving forward through locales. Save points appear frequently in the overworld, refilling the player's health while saving the player's progress.[2]
During battles, the player controls a small heart which represents the protagonist's soul and must avoid attacks unleashed by the opposing monster—in a similar fashion to a bullet hell.[1][3][4] As the game progresses, new elements are introduced, such as colored obstacles which require the player to stand still or move through them, and boss battles which change the way the heart is controlled.[3] The player may choose to attack the enemy, which involves timed button presses, earning EXP and gold for defeating them.[5] Alternatively, they can use the ACT option to perform non-violent actions, which vary depending on the enemy.[4] If the player uses the right actions to respond to the enemy, they can choose to spare them and end the fight without killing them—earning no EXP.[6] The game features various story branches and endings depending on whether the player chooses to kill or spare their enemies, and it is possible to clear the game without killing a single enemy.[7]
Monsters will converse with the player during battle, and the game will tell the player about how they're feeling or what they're doing.[8] The monsters' attacks will change in ferocity based on how the player interacts with them, being easier if the player chooses non-violent options, or harder if the player chooses to fight.[1][8] If the player fights a boss character on a second playthrough, their dialogue will change based on the player's actions in previous playthroughs, including whether they appear at all. The final boss of Undertale is different based on whether the player killed no monsters, some monsters, or all monsters.