Retaining the papacy.

[rhowerin]

Once you become the controller of the Holy See, what's the best way to hold on to it?

 

[Bakenellan]

It is never completely certain, but basically you need to be a large nation, catholic and have a high papal influence to hold papal controller title. For the influence it really helps to be narrowminded, have a few religious NI, and send missionaries as a delegate to pope from religious decision screen. Personally I managed to be a almost constant papal controller only when playing a blobbed Papal State itself, otherwise it comes and goes.

 

[DPS]

Being big is always a huge help, because there's a random factor in where a new cardinal will come from when an old one dies, and the more Catholic provinces you own, the better chance he will be from one of your provinces, just by random luck.