After Finally Beating Fallen Mode In Tower Defense Simulator, you finally broken your Record in 16 Minutes and 37 Seconds to be exact, you suddenly got a Message saying:

"GREETINGS PLAYER. YOU HAVE PROVED YOURSELF QUITE SKILLFUL SO FAR... BUT HOW SKILLFUL DO YOU THINK YOU ACTUALLY ARE? LET'S PUT IT TO THE TEST."

It seems you activated the Hidden wave.

"ARE YOU READY? SEE IF YOU CAN BEAT THIS!"

Then of course the Creator appears not too shortly after.