Undertale for Android is a role-playing video game created by American indie developer and composer Toby Fox. In Undertale for Android, players control a human child who has fallen into the Underground, a large, secluded region underneath the surface of the Earth, separated by a magic barrier. The player meets various monsters during a quest to return to the surface, mainly through the combat system; the player navigates through mini-bullet hell attacks by the opponent, and can opt to spare monsters instead of attacking and killing them. These choices affect Undertale for Android, with the dialogue, characters, and story changing based on outcomes.
Undertale for Android is a role-playing game that uses a top-down perspective. In the game, players control a child and complete objectives in order to progress through the story. Players explore an underground world of towns and caves, and are required to solve numerous puzzles on their journey. The underground world is the home of monsters, many of whom challenge the player in combat; players decide to kill, flee, or befriend them.
When players encounter enemies in either scripted events or random encounters, they enter a battle mode. During battles, players control a small red heart which represents their soul, and must avoid attacks unleashed by the opposing monster in a similar fashion to a bullet hell shooter. As Undertale for Android progresses, new elements are introduced, such as colored obstacles which require players to remain stationary or move through them, and boss battles which change the way players control the heart. Players may choose to attack the enemy, which involves timed button presses, earning EXP and gold for defeating them. Alternatively, they can use the ACT option to perform non-violent actions, which vary depending on the enemy. If players uses the right actions to respond to the enemy, they can choose to spare them and end the fight without killing them. In order for some boss encounters to be completed peacefully, the player is required to survive until the character they are facing has finished their dialogue. Undertale for Android features various story branches and endings depending on whether players choose to kill or spare their enemies; and as such, it is possible to clear the game without killing a single enemy.
Monsters will converse with players during the battles, and the game will tell the players what the monster’s feelings and actions are. Enemy attacks alter based on how players interact with them: should players choose non-violent options, enemy attacks are easy, whereas they become difficult if players choose violent options. Undertale for Android relies on a number of metafictional elements in both its gameplay and story. When players participate in a boss battle on a second playthrough, the dialogue will be altered depending on actions in previous playthroughs.