...definitely from another universe, then. The "coins falling out of the sky" part gave it away.

It also disproved her theory, unless this "Clown Car" crashed into the castle.

Another possible theory was that people who were in vehicles that crashed into things were transported here at the moment of impact. It was a stretch, but it was all she had.

Undyne asked Bowser, "Do you remember anything between your Clown Car crashing, and waking up here?"