Info on how to get a P Rank: https://steamcommunity.com/sharedfile...
Playlist with all P Ranks:    • Pizza Tower - P Ranks  

Getting any rank is acquired by getting enough points in the level. You can get either a D, C, B, A, or S Rank based on your performance at the end. Getting to B isn't too difficult if you're aiming for most of the collectibles in a level, but if you want to hit S rank you will have to pull up some leg work.

To get a P Rank in a level, it is expected that you do the following things within one run of any level:

Kill an enemy before leaving the first room
Get enough points for an S Rank
Find all toppins
Find all secrets
Get the secret treasure
Go through the Lap 2 portal
Never drop your combo once