This is the bestiary diagram.
It helps a lot when you knows approximately all the monsters and their evolutions. To select your starting god, or even when you want to upgrade a monster, you want to use this diagram because it shows you al the evolutions of all the basic monsters, and you can better build your strategy.

Even if it isn't up to date, I highly recommend you to read the following guide because it's in depth guide about the crawl bestiary, furthermore very well done.

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=297570570