After finishing the game without using the "Slow mode" the "Extra mode" (???) will be unlocked. This new mode allows you play the game in different ways. Also, if you beat these levels you'll find out more stuff about Nekomew's story...from a different point of view...

If you have purchased the game in itch.io you can ask for a Steam key sending an email to steamkey@pikewin.com with the subject "Nekomew's Potty Trouble Steam Key"!