Playing Papal States, holy year 1636.
I exploded France very early while they were at war with Burgundy, I then exploded Burgundy, started eating French and Bourbon territories and later exploded England. Austria remained my biggest problem up until around 1550, now it's my infamy. I only need to take Friuli from Aquilea to make the Kingdom of God national decision (which is completely OP).
My constant advance into their territory means the empire is pretty much dead at this stage, never able to get more than 5 authority or something. After all, all matters related to God should be ruled by men of the Church.
My first national value was Unam Sanctam so not being catholic is a very bad idea. Also I'm the forever papal controller (I have like 75% of obtaining the next cardinal, all the time), whenever some catholic nation annoys me I just excommunicate them. Also having all those cardinals gives me -1.2 infamy per year.
I pretty much control all important european COTs except lubeck, and I also formed the first carribean COT in Moron so I get a heapload of gold through trade.
I have a lot of small vassals that I will take some time to annex. France (Calais), England (London), Ragusa, Monteblack in spanish, Alençon, Normandy, Aragon and Algiers. They are all catholic. Even funnier, Algiers is ruled by a bishop.