Undertale Boss Battles Script | 360p 2025 |

Every Undertale fangame starts with the UI script. Here’s a pseudocode breakdown of the battle menu logic (suitable for GameMaker Language or Python/Pygame):

For players who refuse to fight, the battle is a test of endurance. It forces the player to confront a mother figure who is trying to protect them through imprisonment. It is the first lesson: Mercy is harder than Violence. This boss fight scripts the central thesis of the game early on—violence is the easy path, but it comes with a heavy cost. Undertale Boss Battles Script

while True: screen.fill((0,0,0))

Use a (FSM) for the battle loop.

Before we dive into the boss battles, let's briefly overview the battle system in Undertale. The game uses a custom-built battle system, which allows for a mix of turn-based and real-time elements. The player can choose to either attack, defend, or use a special ability during battles. Every Undertale fangame starts with the UI script