I've finally done One Faith after a missed by 3 in-game weeks failure back in September, but I've crowned it with One Culture too.
TAGs: Provence -> France -> Austria -> Croatia -> Sardinia Piedmont -> Italy ->Roman Empire -> HRE
Ideas: Influence; Offensive; Administrative; Religious; Diplomatic; Expansion (abandoned when everything got colonized and replaced with) Humanist; Aristocratic
Started out as Provence, dragged France into a war against England before the Maine event could fire for my core. Took it back, took one province to start a Normandy vassal, gave one province to France so that he'd be satisfied. At the game start Austria was one of my starting rivals (typical), but he either surpassed me or simply switched me to Savoy, which came in handy, because he was now an enemy of my enemy. After the English war I moved capital to Marseille, improved and allied Austria and joined the HRE. Broke alliance with France, ditched Austria, picked up Burgundy, hoping to feed him into France and surroundings, then inherit. Using the Provencal mission tree I reconquered Naples, but missed out on the Aragonese PU because of an early IW. Burgundy became hostile after the second French war, breaking the RM and ruining my inheritance, then promptly died. Austria demanded he release the lowlands, he complied, France attacked for the PU but got his teeth kicked in and lost Paris. Just after the BI went down Austria died young and I got voted Emperor (rubbing in the salt of losing the BI), then very shortly after the Burgundian war France he fell under a free PU with me due to our shared dynasty.
I didn't plan to form France, but getting him into a PU was a nice way to get rid of him, and getting Emperorship meant I couldn't disinherit freely to fish for a Castilian PU, thankfully France has a CB in his mission tree. In the 50 years until I could integrate France I followed the Provence missions, conquering Aragon, PU-ing Hungary. I also started getting into Savoyard lands, used Milan and the Swiss to eat him up for me so I could vassalize an OPM and then reconquest. When taking the Savoyard lands back from the Swiss I allied and called into the war Austria (once he loses Emperorship he likes to eat everything to connect his lands), fed him the Swiss, then with a stroke of genius I unlawfuled him for the Swiss lands. He felt a big boy and said no, so after the truce I promptly dismembered him using the Imperial Ban CB, releasing Tirol and Styria, which because of the never going away free guarantees he didn't dare to touch again.
Meanwhile the reformation was also happening, Bohemia turned full hussite with a center (second time I've seen it happen in one of my games since it has been introduced, first time when I was also in Europe), which thankfully mostly molested Poland, eventually turning him into hussite. I dealt with the other centers more or less pretty quickly, but Bohemia was huge, bigger then to enforce religion. IA gain was in the gutter, I barely managed to pass reforms, and I was gunning for Erbkaisertum so that I can kick heirs for potential PUs, most notably Russia. Bohemia somehow lost a war (I didn't pay attention, I was crusading the Ottomans), and was forced to release his starting vassals plus Moravia. This finally meant that I could declare on him using the Hungarian permaclaim and enforced religion, preventing the League war from ever happening.
Picked up Russia as an ally, he naturally got my dynasty, so when the first opportunity arose I pounced and PU-ed him. Followed the French missions, PU-ed Castile (who at one point had Portugal but lost him, and despite the domineering AI didn't go for it until the CB expired), and, thanks to my Ideas, the age of reformation ability, the Council of Trent and the Malta fort I actually used the French Subjugate CB against Poland, who stretched from the Baltic to the Black Sea, but has eaten into the Ukraine because went with the local noble at the game start and eventually fell out with Lithuania.
Once I had the Castilian PU, it was time to get rid of Austria, so I could reform him for his missions. I diplo-vassalized Tirol and Styria, took Wien for myself and gave the rest to one of the Bavarian minors. Integrated the vassals, formed Austria, did it's more important missions (kicking Ottomans out of Europe, getting the Imperial Austrian Monarchy government reform and so on. When I was done, flipped Croatian, mainly for the permanent -5 years of separatism modifier, then formed Sardinia Piedmont, did the missions, formed Italy,, conquered into England, integrated Castile, ate mainland Portugal, formed Rome but kept Italian ideas, then finally I was done and unified the HRE, because didn't really want to abuse the vassal swarm, and switched to HRE ideas.
This was 1647, I had -55% CCR, -90% integration cost and 60% admin efficiency form missions, monuments, absolutism, etc. And then the fun began. With 16 month coring cycles, I basically conquered the rest of the world by 1744. using a combination of direct conquests and catching and releasing huge, culturally homogenous vassals to use for helping out in conversions, Up until that point, I only had Europe (plus the parts needed for Rome from England, Africa and the Middle East) and had a Russian PU. Once Imperialism hit, I conquered and released/consolidated: Songhai in Sub-Saharan Africa, Kilwa in East Africa, Kongo in Central Africa, Chagatai for the Oirat region, Manchu for Manchuria, Japan, and since Ming was dead, I got Wu for China. The rest I conquered and cored directly. Moved capital to Australia for the true one tag, ate up the Americas, and finally finished the WC in 1744. One faith was done except for one province with expelled minorities until 1758, so I integrated my subjects and set out to culture convert the world to Roman.
I chose Piedmontese for the culture to flip to Roman, so I was spreading it quite early where I could from the moment I got my hands on some of that clay. Maxing out the culture conversion reduction was possible in earlier patches too, but with the introduction of monuments, and as of 1.32 the estate privilege (I did not use it, but it was there should the need have arisen) getting to the floor is trivial nowadays. I finally finished in 1805, could have managed it a little sooner, but I mistimed how much more would I need to start all conversions before I convert Kotagede, since you lose out on the monument once the province isn't Javanese anymore.