First, make sure you have all the previous Keys. Then, talk to GPB in the Void Room and try again. If it still doesn't spawn, you've already collected it.
It's probably fake. Click here for a list of fake Keys.
See below or click here.
Just keep trying, you’ll get it eventually. Also, be sure to leave the room and come back after talking to him 6 times in a row.
There’s one main requirement: your rank on every level. If you don’t care about the technical details, getting at least a B on every level (not including Arenas or Death Mode) will suffice.
Unlocking CToP works off of a “points” system. Your rank on a level gives points, and your total score is what determines if CToP is unlocked. P is 5, S is 4, A is 3, B is 2, C is 1, and D is 0. An uncleared level counts as negative 4. To unlock CToP, you need at least 40 points total across all the main levels, not including Arenas or Death Mode. Once you meet the requirement, it can be accessed on the Top Floor by going through the door to the right of the Arena.
Simply P rank The Crumbling Tower of Pizza.
If the error description is “Data structure with index does not exist”, it's because you're using someone else's save file. Hope you made a backup!
Enter the doorway next to the elevator on any floor.