Roboquest

Billy Boom is a boss in the Ruins Biome, he is a big round and red boss, you get the Ruins key after defeating a boss in the first area, and the Ruins can be accessible about halfway through the Canyons Biome (first area)

To trigger Billy Booms explosion, all you need to do is stay close to him, it will fill a bar up that's underneath his health bar and it will trigger a cut scene and will end your run with you dying