Knocked out the One Who Brings Benefit achievement. Only one more day to go too.
Earliest start, chose the duke of Dailam or whatever it's called, died early (Which wasn't intended), falsely gave up Zoroastrianism, started a cult, spent the next 2 centuries slowly swallowing up the de jure lands of the Persian empire. Once I had almost all of them (I was missing a duchy the caliph was personally holding) I declared an independence war. I hadn't even checked, but by pure luck they were in the middle of helping deal with a crusade and as soon as I declared they attempted to revoke Syria, resulting in them dealing with a second revolt war. Kicked their arse quite handily, formed the Persian empire, brought the cult out of hiding, gave out king-tier titles to a few people, forced rulers to convert en masse (Since only half of my vassals were cultists), keeled over dead (which was useful since it meant my truces vanished), took Arabia in a GHW, took the last two duchies I needed (Abbasids and Tibet owned them) and by that point I had the 1500 piety I needed. Renamed my dynasty to Sassanid and changed it to the Sassanid flag, because like fuck I'm not reclaiming the legacy of my ancestors.
Next step: Wait for China to get out of its golden age and force them to open. I've learned how to savescum even on ironman (Only used it once, which was because the game threw that BS "Knock-knock it's death want to play chess?" event at me at, as the game likes to do, the worst possible time) so for shits and giggles tried to force them open. I had 48k, they summoned 100k