Complex sentence: Monika then speaks audibly to the player (the only spoken dialogue in the game) and sings a song she had been preparing, which plays over the credits (which display all of the scenes the player failed to witness).
Split into simpler sentences: Monika then speaks audibly to the player (the only spoken dialogue in the game). She sings a song she had been preparing, which plays over the credits (which display all of the scenes the player failed to witness).